Reinforced Concrete Construction Failures Exposed by ... · public education about seismic risk and...

Reinforced Concrete Construction Failures, January 2019 By: Ing. Sjoerd Nienhuys www.nienhuys.info

1

Reinforced Concrete Construction Failures

Exposed by Earthquakes and Other

Examples of design errors and

wrong work execution by building contractors and

lack of quality control or on-site construction inspection

Report by: Sjoerd Nienhuys

Architect, Seismic Engineer

Report date: January 2019

http://www.nienhuys.info/


2

Table of Contents

1. Not Applying the Relevant Building Codes ................................................ 3

2. Learning from Mistakes ............................................................................. 4

3. Earthquake Movements ............................................................................ 5

4. Not Adhering to Basic Design Recommendations ...................................... 6

5. Causes of Reinforced Concrete Building Failure ......................................... 7

6. Ductile Zones in Columns ......................................................................... 11

7. Beam-Column Anchorage ......................................................................... 11

8. Concrete Casting Quality .......................................................................... 13

9. Overload and stiff floors .......................................................................... 14

10. Columns Must be Stronger than Floors .................................................... 15

11. New moment areas .................................................................................. 16

12. Construction Details ................................................................................. 16

13. Building Materials, Aggregate and Water ................................................. 18

14. Smooth and Profiled Steel Bars ................................................................ 20

15. Government or Private Control on the Design and Execution ................... 21

16. Thin Flat Reinforced Concrete Roofs ........................................................ 22

17. Prefabricated Lightweight Wide-Slab Floors (BubbleDeck) ....................... 23

18. Structural Safety Resume ......................................................................... 25

ABSTRACT

After earthquakes it becomes very visible what types of building construction have withstood the forces

of the earthquake and which did not perform adequately. Analysing the nearly collapsed and broken

reinforced concrete structures, gives a good insight in the possible architectural and engineering design

mistakes, faults in the detailing, lack of on-site inspection and rectification, or the mismanagement of

the construction by the building contractors. For reinforced concrete construction, mainly inadequate

column designs and over-weight structures are the cause of fatal building failure, collapse and related

human victims. Heavy and stiff floor constructions are not useful for the overall strength and ductility

of the reinforced concrete buildings. Inadequate execution skills and non-expected thermal expansion

are other problems. The paper gives a dozen examples from different countries, illustrated with photos

and sketches.

Key words: earthquake, building design, failure, columns, reinforced concrete, stirrups, pancake.

Sjoerd Nienhuys

Architect, Seismic Engineer

E-mail: [email protected]



3

1. Not Applying the Relevant Building Codes

Only after the occurrence of an earthquake it can be seen if the buildings have performed adequately

according to their structural design. The design criteria, however, may be different for each type of

building, especially when no binding national Code exits that defines the minimum strength.

The Seismic Code, or earthquake resistant building code may vary per country, but usually defines the

seismic zoning according to history and the latest knowledge. Many countries, however, have many buildings that were constructed under older versions of the Seismic Code. Generally, these older

buildings are seldom upgraded, basically because of the high costs involved. Yet, when the buildings

are designed and constructed according to these older Seismic Codes, they will most likely not fatally collapse with an earthquake of the maximum design magnitude (for the given zoning).

The 12 January 2010 earthquake in Haiti (Léogâne) had a magnitude of 7 Richter. With a shallow depth

of only 13 km under the city of 2 million inhabitants it resulted in massive damage and somewhere

about 230,000 causalities. Another large earthquake occurred on 27 February 2010 in Chile (Maule

region, Cañete) had a magnitude of 8.8 Richter. The two are compared below.

The differences in death tolls are significant and caused by the following characteristics:

# Haiti, 12 January 2010 Chile, 27 February 2010

1 Force earthquake 7 Richter with PGAg 0.44 Force earthquake 8.8 Richter with PGAg 0.65

2 Depth 13 km (shallow) Depth 35 km (moderate deep)

3 Right under the village Léogâne (10,000), and only 25 km from capital Port-au- Prince with over 2 million inhabitants.

Concepción at distance of 115 km. More than 50% of

causalities caused by tsunami crushing into small coastal

villages, 109 km from Talca.

4 54 aftershocks 4 Richter and greater with two

of magnitude 5.9 Richter.

Maximum aftershock 6.2 Richter.

5 Over 222,000 deaths. Over 1.2 million people

homeless

Over 500 deaths. 2.1 million people homeless

6 Poor quality houses not build according to any

earthquake code.

Better quality houses, most were build according to the

latest Seismic Codes.

7 Many single storey adobe houses in town,

having a loose structure and large mass.

Single and two-storey houses. House destruction

directly along the coast also by the tsunami.

8 No Seismic Code, no existence of any

government control on building practices and

substantial corruption.

Existence of Seismic Code, training of skilled workers,

government control on designs and control on building;

little corruption.

9 No history of large earthquakes and no

information available on better designs.

History of very large earthquakes in same region and

available documentation with design pictures.

10 Large amount of informal building without

involvement of architects and engineers.

Training of architects and engineers include the

application of the most recent Seismic design Code.

Although the earthquake in Chile was much stronger than the one in Haiti, the better construction practices (adherence to the Seismic Code), and lesser population nearby are part of the much smaller

number of causalities1. The large casualty in Haiti is a result of a long-time dysfunctional government structure since it gained independence half a century ago. The failed-state situation causes lack of

training of engineers and architects and a total lack of control on what was/is being build.

1 https://www.researchgate.net/publication/305537765_Seismic_Building_Codes_in_the_Himalaya_Region_Questions_Answers_Related_to_the_2015_Nepal_Earthquake


https://www.researchgate.net/publication/305537765_Seismic_Building_Codes_in_the_Himalaya_Region_Questions_Answers_Related_to_the_2015_Nepal_Earthquake

https://www.researchgate.net/publication/305537765_Seismic_Building_Codes_in_the_Himalaya_Region_Questions_Answers_Related_to_the_2015_Nepal_Earthquake


4

Comparing and analysing these two earthquakes and the physical damages caused, shows the

significance between (1) good governance (having Seismic Codes and applying them) and (2) technical

training of building professionals. This was possible because (3) earlier earthquakes occurred recently

in Chile, and (4) the absence of these three factors in Haiti. However, it is widely known that Haiti lies

in a high-risk earthquake zone, but with no recent earthquake history (measured in human lifetime),

no attention was paid to that high earthquake risk. Massive population growth combined with a poor

economy, both caused by poor government, allowed the development of the large slum settlements.

Although this paper looks at typical design and construction mistakes, these would not occur when

public education about seismic risk and construction technology exists, and also not when there is an

adequate on-site control on the executing of the buildings. By analysing the technical aspects of failed

buildings a high learning curve is achieved, higher than only studying what is the right way. By studying

and exposing the details of collapsed buildings, those information’s are generally better imprinted in

the brains of the designers than those of the still standing buildings.

2. Learning from Mistakes

Any learning process has different components through which that learning takes place. School

learning may be based on book knowledge, theoretical explanations and study, but most people learn

more from real examples and learning by doing. Seeing is also much more educative than just reading,

reason for which the illustration of a topic is of great importance in the learning process.

Analysing post-earthquake pictures does vividly teach about what designs were faulty and why. Unfortunately, that cannot be said from the structures that were not damaged, because from the

outside little can be seen. Only the study of the drawings and calculations can determine why a certain

structure did not fail1. It is easier to understand why neighbouring structures were damaged or totally

collapsed. In particular those constructions that remain standing, just before their point of total failure

are interesting, because they present themselves as a freeze-frame during the process of collapse.

Photo 1. Balakot, Kashmir.

The picture shows the stilled moment, just before

the total collapse, indicating where exactly the construction failed. Analysing the reinforcement

will indicate why it failed.

In the following paragraphs some picture material

is shown of earthquake damage and commented upon.

Also some information is provided about constructions that have either good or bad designs. The

information is not at all exhaustive or complete in all details, but it provides some very common

examples that can be found in many cities, after disasters in earthquake zones.

1 Studying and acknowledging mistakes and errors, and subsequently make the legislative and technological improvements widely known, is more productive in the long term than trying to avoid publication of the errors. Not all countries will have the economic possibility to retrofit all existing buildings, but better training of the controlling staff and skilled workers, as well as better on-site supervision will avoid building poor constructions.



5

3. Earthquake Movements

Buildings are primarily designed to carry their own weight and the live load caused by occupants. The own building weight (vertical load) is often the most determining factor in the design. The vertical tremor component “P” of the Rayleigh movement, is easily withstood by most buildings. Buildings that are located away from the epicentre, will receive an increased lateral rocking type force, moving the building forward and backwards, often causing major damage. The amount of horizontal earthquake force that takes effect on

the foundation depends on the Peak Ground Acceleration (PGA). Buildings in different locations or on different soil structures can be subject to each a different PGA.

Figure 1. Schematic presentation of the different vertical and horizontal movements..

Buildings in an earthquake are subject to a combination of the waves indicated in the picture. The

wave length (horizontal component of the Rayleigh type wave) and with that, the time between

forward and backward movements, will increase with the distance from the Epicentre. With increasing

distance from the epicentre ( > distance hypocentre-epicentre) the wave amplitudes will diminish.

The seismic building codes are based on an calculated balance between the risk of a heavy earthquake occurring in a given location, and the very high economic cost of making every construction fully

damage resistant. The Seismic Code recommends minimum construction standards to avoid total

building collapse, and allows people to survive1, even if the building is economically a total loss.

Building with brick and concrete to withstand a Richter 8 earthquake without any damage is

economically very costly; the alternative is a very lightweight and ductile structure, or using base-

isolation. Base-isolation is widely practiced for high buildings, but for low and wide buildings it is expensive because of the double foundation structure.

Figure 2. Effect of base-isolation.

The accelerated horizontal movement (PGA)

and the inertia of the building mass, causes

horizontal loads on the building in proportion to its mass and the acceleration. With base-

isolation these forces are almost eliminated.

The base-isolation can consist of rollers or flexible rubber supports and combinations thereof. The

horizontal ground movement takes place with causing only a very small horizontal load on the top building foundation, causing the building to stands almost still on the fast moving base-foundation.

Due to only small forces, the structure’s strength can be economised as compared to the left design,

but foundation costs are substantial higher. For tall buildings in earthquake areas this is a common

practice. Constructing base-isolation under existing buildings is complicated and costly.

Famous quote: “Earthquakes seldom kill people, but collapsing building do”.

1 Generally people will not have the time to run out of a building during an earthquake. It is also dangerous because of falling pieces. Therefore the building should not collapse during the first heavy part of the earthquake.



6

4. Not Adhering to Basic Design Recommendations

Reinforced concrete is called “modern” building material in the eyes of many people, especially rural

people, because they see large town buildings going up in reinforced concrete. However, reinforced

concrete is very heavy and therefore not a suitable material for lightweight construction. Secondly, the quality of the reinforced concrete depends on the design and the location of the reinforcement,

as well on the cement and water quantities, composition of aggregates, casting method and the

curing. With a good design, but poor quality work implementation, the concrete does not have the required strength. It causes unbalanced interaction between the steel (stress resistance) and the

concrete (press resistance), resulting in a lower structural strength than the proposed design.

People like to build in reinforced concrete because the material has the image of durability due to its

use in expensive buildings in large towns. It depends however, on the detailing of the reinforced

concrete, the earthquake force, and the distance to the epicentre whether the heavy reinforced concrete building will survive. In many cases reinforced concrete is the largest earthquake hazard.

Photo’s 3, 4 and 5. Nepal

In rural Nepal contractors with some town experience, started to build reinforced concrete support

structures. In town, near the epicentre, several of these buildings collapsed due to faulty design of

ground floor columns. Removal of ground floor shear walls to create open shops (middle photo) is a

common situation in both rural and urban situations, affecting the overall stability of the building.

Photo 6, Nepal

Basic design guidelines such as the width of the building or the proportion of

the overhang over the foundation, are not adhered to. With the common

square section columns, this building would have collapsed when the

earthquake was in the left-right direction.

Figure 3.

The columns in this building should be

rectangular to better withstand the

lateral forces on the building.

In this case, the municipality should not have given a building

permit for the realised height or width of the building. In

many cases owners do not adhere to the regulations and add stories to buildings that have only lower permits.1

1 Detailed recommendations about seismic resistant construction are provided in the document: https://www.researchgate.net/publication/281898976_General_Rules_for_Seismic_Strengthening_of_Buildingspdf


https://www.researchgate.net/publication/281898976_General_Rules_for_Seismic_Strengthening_of_Buildingspdf


7

5. Causes of Reinforced Concrete Building Failure

There are often several reasons why buildings will fail when the forces on those buildings are still

within the maximum earthquake design force. In analysing the causes of collapse, several can be debit

to the failure. During the forensic analysis, the wider aspects need to be investigated to draw lessons on how steps in the entire building process must be improved, to avoid similar disasters in the future.

History, education and legislation:

1. When a country (during human lifetime) is not affected by earthquakes, the tendency exist

not to pay attention to the potential danger1. Subsequently no seismic code is developed2.

2. When no seismic or general building code exists (like Haiti), there is also is no relevant legal framework, and nobody feels the need to adhere to out-of-country codes2.

3. Without building codes, the education of construction workers in this field is absent. This

applies to the architect, engineer, municipal supervisors, mason and concrete worker.

4. In rural areas self-help builders and local contractors may not be aware of any codes. Often

non-qualified staff or supervision exists to guide the builders on-site in these matters.

5. Often no knowledge exists about the soil structure or constructing on unstable slopes.

The technical design:

6. The designs are architecturally not always adequate for high risk earthquake areas. In some

countries the architects do not have adequate engineering design training and rely on the engineers to fix their designs according to the strength requirements of the Seismic Code. In

Latin America there is too often no coordination between the architects and engineers, but

the engineer is made responsible for the correct design strength.

7. The engineers have not always indicated the correct reinforcements at the correct positions.

The drawings of columns and other reinforcements are not always individually detailed.

Specifications need to be presented in drawings and these need to be present on the building

site. Site inspectors and construction workers need to be able to read these drawings.

8. For reinforced concrete building components, the architects and draughtsmen do not detail

the reinforcement or make for each drawing detailed charts for the steel cutting and bending.

9. In rural areas often no structural designs or calculations exist; contractors build on the basis

of their experience, using standard column sizes for all columns and floors.

The construction work:

10. Building contractors may not adhere to the steel quality specified or reduce the dimensions,

or leave out a number of bars. When fitting problems occur, they do not feed back to the

engineers who made the drawings, but make their own on-site solution (leaving out bars).

11. Contractors may use inadequate quality of aggregates such as sand (dirty), stones (weak), and

water (salty) and cause improper mixing (by hand) or add too much water (W/C factor). In

very hot or cold weather often too many additives are added, lowering the cement quality. Inadequate curing (keeping wet) is a common in hot-sunny countries.

12. Poor quality formwork and insufficient cleaning of the formwork may cause dirt and binding

wire cuts to remain, improperly placed spacers, causing corrosion in the long term.

13. No or inadequate vibration of the freshly cast concrete may cause low pressure resistance or

the creation of honeycomb concrete around the reinforcement bars.

1 For Kathmandu, the interval period for the mayor earthquake was long time ago established at 75 to 80 years. However, in the last three decennia, a large number of multi-storey buildings were erected that did not comply to the Seismic Code for the region. Lack of training and code enforcement are here part of the problem. While other large earthquakes are predicted in the western section of the Himalayas of Nepal, the country or the people do not have the economic possibilities to retrofit the millions of substandard houses. 2 This was the case in Haiti and other Caribbean islands. The USA related islands had the American Seismic Code.



8

14. Wrong sequence of the construction, by which top heavy building sections are realised

without adequate stability measurements in the lower storeys.

Inspection of the work:

15. With an inadequate legal framework for work inspection, this is either not done, too late or

building inspectors are rubber stamping designs and inspection reports, without physically being on-site the day before the concrete is cast. In rural areas (municipal) control is often

non existing or poor. Building inspectors being paid off by the contractors is common.

16. No on-site control allows the building owner to add one or two stories to the building, thus affecting the load factors on the building. After multi-storey buildings are completed and

sometimes increased in height, the ground floor is often opened up by removing inside shear

walls to have more shop area.

User modifications:

17. Building owners, once occupying the building, make non-approved modifications in the

ground floor such as removing shear walls to create larger open areas for shops and garages.

The above list of is the result of lack of standards, lack of education and a failing supervision system,

deficiencies that can be regularly found when inspecting post-earthquake damage. A combination of several of these points was the outcome of the author’s investigation of the Ecuador, Esmeraldas

earthquake in 1976, and some other points in the Balakot, Kashmir earthquake 2005. In 2005, he worked in the tsunami reconstruction programme in Sri Lanka and Indonesia. In Indonesia the

problem of earthquakes was all present, but still some errors were found in the ongoing re-

construction process. In 2015 an assessment was made of the large earthquake in Kathmandu, Nepal.

Also here many prominent examples were shown of not adhering to the old seismic code, and applying

posterior modifications to buildings with the result that they collapsed.

Photo’s 7 and 8.

Balakot,

Pakistan 2005. The assessment

was that many

buildings were constructed on

the base of “contractor

experience” without calculations, and without adherence to the available Seismic Code. The Pakistan

Seismic Code was only practised in the main cities.

The 17-point list indicates the possible dangers in the use of reinforced concrete, and emphasizes that

good quality control is required for every step. A particular problem of reinforced concrete is that once

it is cast, it is difficult to assess the quality of the concrete or the reinforcement inside. Seeing concrete

columns and beams on the outside does not guarantee a good quality construction, unfortunately

some “reinforced concrete” buildings are a simple death trap during an earthquake.

The earthquake of 9 April 1976 in Esmeraldas, Ecuador had an estimated force of VI on the modified

Mercalli scale or approximately 5.5 to 6 on the Richter scale. Some damages depicted below are from reinforced concrete buildings that were in their construction phase. Because of the available

reproduction possibilities in 1976, the most significant pictures were re-drawn in pencil.



9

Photo 9. Esmeraldas

This was a line of shops, being fully

pancaked due to failure of the ground-floor

column structure.

The building was realised (1950?) without

any consideration of any seismic code.

Heavy concrete roof. No internal shear walls

existed to withstand lateral forces1.

Photo 10.

Close-up of the left of this building, showing the

20 cm thickness of the reinforced concrete floors.

This was increased by another 8 cm cement top

floor. Total mass of > 670 k/m2.

With a size of 9m x 30m or 180 ton per floor, the

result is a massive horizontal load during an

earthquake. Only very well designed and

anchored shear walls from foundation to the

roof can resist such a force.

Photo 11.

A block of new apartment buildings under

construction, being totally flattened as a result of

the absence ground floor shear walls.

The block was in its construction phase and the

contractor had not yet realized the infill walls on

the ground floor, while the first floor was already

loaded with masonry for facades and separation

walls. In this case the planning or the construction

phases in the building process had not considered

that the area is a notorious earthquake zone.

Photo 12.

The same apartment building.

Because in the first floor, the inside infill

walls were already constructed this section

came down as a whole. However, the

ground floor section was planned as open

shops, having no or inadequate number of

shear-walls in the length of the building.

1 In a further investigation it was found that large numbers of new social housing in Quito, had similar design problems. Making this officially known would cause a huge political scandal and possibly bankruptcy of the national social security institute. The INEN (Standard Institute) decided to keep this quiet and embark on improving the national Seismic Code according to the American ACI 318 and the related legal framework.



10

Photo’s 13 and 14.

This section just did not collapse, but will do so with the

next aftershock.

The weakest areas in the construction are the maximum

moment forces at the bottom and top of the ground-

floor columns. Concrete quality was too low, while no

confinement or caging exists in these maximum

moment areas of the columns.

Figure 4. Lack of confinement.

The strength of reinforced concrete is the

result of the interaction between the

concrete, providing resistance to

compression, and the steel giving

resistance to tension. When the concrete

crumbles due to exceeding forces or poor

quality, it will fall away and stops

interacting with the steel. The steel will

buckle and the building collapses. In both

urban and rural buildings this common design mistake (e.g. not

designing sufficient stirrups in the maximum moment areas), is

one of the most frequently encountered errors.

Figure 5. Confinement in the maximum moment areas.

The mass of the building is moved horizontally because of the earthquake. When the earthquake forces exceed

the actual compressive strength of the concrete, the

alternating forces of the earthquake stretch the steel on one side and compress the concrete on the other side,

breaking the concrete. By repeated movements and lack of stirrups, the broken concrete will fall out of the

construction and the steel will bend, becoming useless.

Figure 6. Process of crumbling



11

6. Ductile Zones in Columns

All seismic codes now specify additional stirrups in the maximum moment areas (columns and beams)

to make them ductile. The above drawing is from the ACI 318, and being widely copied. Because the

failure of columns has a more disastrous effect than the failure of beams, strict adherence to the

column confinement of the Seismic Code is vital. In the event that the maximum earthquake occurs,

the concrete may crack but stay in the cage, providing resistance to the load. Because of the movement

of the building, some of the earthquake impact will be absorbed, allowing the building to remain

standing, and allowing the occupants to evacuate. In some cases the building may be economically

lost, but in other cases the cracked columns can be repaired and strengthened.

Photo’s 15, 16 and 17. Repair of cracked areas in columns. Two-

component epoxy is injected. The columns are also increased in size.

Photo’s 18 and 19 (BBC report

of the Kathmandu earthquake)

Although the additional stirrups

are “only a detail”, it depends

on these details whether or not

a building will remain standing

after an earthquake.

7. Beam-Column

Anchorage

Photo 20. No anchorage.

Figure 6. Drawn detail.

The lack of adequate anchorage between the support beam and the column allows the beam to be

disconnected from the column. It is possible that the design drawings did not specify the anchorage of the reinforcement bars, or that the contractor did not put them in according to correct drawings.



12

These kind of details indicate the need for precise control of the design as well as on-the-job

verification of the reinforcement BEFORE the concrete is cast.

Profiled concrete reinforcement bars provide better adherence and anchorage in the concrete than

the older type smooth steel bars. However, they are calculated in smaller dimensions because of their

higher strength. The enveloping concrete must also be of the correct strength; if not it will crumble

and adherence will be totally lost. Hooks will provide extra length and security against pull-out.

Figures 7 and 8. These drawings were made from photographs,

demonstrate the lack of anchorage.

The minimum anchoring length of the bars linking beams to

columns is specified in both the general Reinforced Concrete Codes is minimal 30 cm.1

The vertical sections of the reinforcement bar (sketches below) should be minimal 12 x the bar diameter. Technical drawings

should be verified by qualified engineers. Reinforcement

drawings should have detailed cutting and bending schedules that can be followed by the iron workers.

BEFORE the concrete is cast in situ, a detailed inspection

should be realised of all bars fitted in place, as well as the

quality and cleanliness of the formwork.

Figure 9.

Anchoring length of bars in

corners.

When in a corner of a reinforced concrete building two floor beams join at a corner column,

crowding of the bend ends of the reinforcement bars can occur. In this case the structural engineer

must specify which of the horizontal bars are needed to withstand the maximum moment forces. In

case of overloading during an earthquake, the beam ends should fail (bend) before the columns.

Photo 21. Overcrowding reinforcement bars.

Four problems are shown here.

(1) The vertical bars of the column are smooth, softer steel than

that of the beams. The beams are stiffer and stronger than the

columns.

(2) All the end bends of all the beam bars may prevent good

filling of concrete around them.

(3) The end of the columns or beams do not have additional

stirrups.

(4) because the floor is integrated in the beams, these will be

more stiffer and stronger than the columns.

1 The Seismic Code is an extension of the General Building Code. Repeating general specifications on reinforced concrete, concrete mixtures and steel reinforcement therefore do not have to be included in the Seismic Code.



13

During an earthquake the short columns will most likely break just under the upside floor beam and

above the low-side foundation beam, possibly leading to collapse. The sketches below explain the process of failure during one forward and backward movement. In reality, a series of shocks occur

during an earthquake, repeating the depicted process and resulting in the column collapsing, and with

that bringing the building down.

Figure 10.

Columns are weaker than

the floor-beam structure

and will fail with an

earthquake.

The sequence shows the

progressive failure.

Figure 11.

When the upper columns have a masonry

infill, this will support the columns in the

event of a maximum earthquake.

The columns under the building often have

the same cross section and reinforcement as

the buildings above the floor, but have the

full building load.

These columns need the caging according to

the Seismic Code to avoid collapse.

Figure 12. Columns stronger than floors.

In earthquake technology the beam-floor

construction should be more ductile, or more

flexible than the column and wall structures.

When the columns or shear walls fail, the building

will collapse. When the floor-beam bends too

much (crack) it will remain hanging between the

columns and people can evacuate the building.

8. Concrete Casting Quality

Large aggregates cause ‘honeycomb concrete’. For casting columns, funnels are required to avoid that

segregation will occur. In the bottom of the formwork for the column, usually a cement and fine

aggregate paste is applied first. These are basic construction skills that should be known by any

contractor and concrete worker. The contractor should have funnels on site when columns are cast.

Although the steel quality is usually a constant factor when supplied from a tested source, the quality

of the concrete itself depends on many factors on- and off-site. From the aggregates, water, cement,



14

formwork, to climate and curing. While testing the concrete quality in collapsed buildings, invariably

the concrete is seldom of the prescribed design quality. For this reason pre-testing of the concrete

mixture at the factory and on-site inspection is important before and during the casting of the concrete.

Photo 22. Poor concrete casting methods and

subsequent poor concrete quality. Photo 22. Collapse. Floor is hanging down.

9. Overload and stiff floors

Making larger floor spans, but economizing on formwork and concrete is sometimes done by placing

hollow cement blocks as infill material. This creates T beams, but also adds mass.

Photo 23. Infill hollow cement blocks

Three problems are introduced.

(1) When the concrete floor is cast, large

amount of thin concrete will disappear

inside the broken cement blocks.

(2) The own mass of the floor will be higher than

when fibreglass cassettes or Expanded Polystyrene,

EPS is used.

(3) The stiffness of the floor is increased which may

be also disadvantageous in an earthquake area in

relation to the columns.

Photo 24. Collapsed overweight floor

This photo was taken in a section of the building which was not yet build up to the second floor,

showing the design of the floor with the hollow cement blocks. Apparently the T beams were not yet adequately hardened (but the supports already removed) when the earthquake struck.

Figure 13. Detail drawing of double hollow cement block infill floor that collapsed during an earthquake.

The sketch is made from another photo. Like in the photo above it was observed that the large weight of the infill floor

pulled the double reinforcement bars out of the narrow

concrete T beams in between the infill blocks.



15

10. Columns Must be Stronger than Floors

Multi storey or apartment buildings tend to have slender columns using little floor space. In addition

they require long floor spans, also minimizing the amount of columns. To minimise also the amount

of beams, the floors are made with a high profile and therefore are becoming stiff.

Figure 14. Effect of stiff floors with thin columns

In the upper line of sketches the building has thick and therefore stiff floors with slender supporting columns.

During an earthquake the bottom columns receive the

largest forces and bend; walls between windows crack and

the whole building will pancake.

In the second line of sketches the floors have a ductile design, allowing to absorb some of the shock. Floors will be

waving and cracking. With properly designed columns the

façade may crack under and above the windows, but the building would not collapse and people can evacuate.

Multi-storey buildings with floors being stiffer than the columns, and when the columns do not have a

ductile design, these buildings have a higher risk of collapse and pancake than with ductile beams; they

may cause the death of the occupants. This is especially so when the ground floor does not have any

shear walls. Linking columns to infill walls strengthens them.

Photo 25. Simple construction design.

This type of reinforced concrete floor, beam and column design

is very common in all villages. Infill walls will in most of these

cases provide support to the columns, but not when there are

windows. There are no anchors in the columns, meaning that

the eventual infill walls are not attached to the columns.

Photo 26. Common design in multi-storey

construction.

From the photo it cannot be assessed if

the columns have the prescribed larger

number of stirrups in the maximum

moment zones, directly joining the stiff

beams. The beam-floor is definitely stiffer

than the columns.

Photo 27. Failed ground floor column in five storey building.

Only after the earthquake it can be seen that failure of the column is caused by the lack of stirrups

and poor concrete quality. In the case sufficient caging existed the cracked column could have been

injected with a composite mortar and covered, or further strengthened. In such a case the building

would have been safe for use. Now the entire five storey building has to be demolished.



16

11. New moment areas

When in a reinforced concrete construction with columns infill walls are placed between the columns,

these can reinforce the structure. The infill walls can dampen the horizontal movement during an

earthquake. However, when the infill walls are only half high, the same wall will cause a new

maximum moment area in the middle of the column height. When the column reinforcement has not

been increased and caging with additional stirrups is provided, these columns may fail first. The angle

of deformation of the free section of the column, above the infill, will be larger than the angle of

deformation of the whole free column. The shorter the free section is, the larger the deformation.

Figure 15. deformation above the infill wall.

When strong infill walls are not taken into consideration

with the design of the columns, these walls may create

an additional large moment area in the un-caged area of

the column. Because the horizontal displacement of the

free area of the column is the same as the entire column,

the deformation is larger, causing additionally large

moments.

Although the building design may have been adequate

without the infill walls, not considering these may weaken the entire construction. Good coordination

between the structural engineers and the architects about the infill walls is essential here.

12. Construction Details

A large building, still under construction, had

a design mistake in the upper floor dilatation

joint. Due to the different horizontal

movements of the two building sections 1 ,

one line of supporting columns broke at their

basis. Also the supported roof construction

was damaged.

Photo 28. Cracked columns supporting the roof

Figure 16. Wrong design of dilatation.

The sketch shows the design detail of the

upper floor, where the columns of one section

were constructed on the other building

section. With the earthquake the buildings

sections moved independently and

differently, braking off the columns and roof.

1 The minimum space between two building blocks is related to their height and specified in the Seismic Code.



17

Photo 29. Detail of column base.

The photo also shows that in the base of the column no

additional stirrups were placed to realise a confinement. This

apparently was the case throughout the building. With a

slightly larger earthquake, the entire building would have

collapsed. At the time of the investigation, no plans existed

to adjust the identified problem.

Photo 30 and Figure 17 from the same building

A solid, heavy concrete

awning above the building

main entrance.

The vertical earthquake

movements caused large

additional forces on the

columns. The standard size columns were not

designed to withstand these additional forces and

collapsed, taking a whole section of the three storey

building down.

Several measurements would have avoided the above type of damage:

A. Stronger columns that can withstand the additional forces. B. A much lighter construction, hence the earthquake force will be much smaller. C. Hanging the awning suspended from the floor above, causing less forces on the columns. D. Having a couple of support columns under the outside of the awning. E. Having the awning separated from the building, not being attached to the columns.

Figure 18.

Different

Options

for the

structural

design.

Photo 31. Staircases.

Staircases should continue to be functioning as an

escape route during and after an earthquake. In

some designs the entire staircase construction with

its walls provide stability to the building as a whole.

Diagonal forces that follow the staircase can

negatively affect the strength of the support walls,

but can also function as a diagonal bracing of the

walls. This all depends on the reinforcement design.



18

Figure 19.

Depending on

the design, the

forces may

affect the

support walls.

13. Building Materials, Aggregate and Water

As indicated earlier, poor quality building aggregates will result in poor quality concrete, not having the

planned compression resistance of the calculations. Salts in the water, sand or aggregates of porous

concrete may attract moisture and cause corrosion. Porous concrete can be caused by incorrect grading

of small and large aggregates, or inadequate densification (vibration) during the casting.

Photo 32. Sand being collected

from the sea shore for reinforced

concrete and masonry mortar.

The salts in the sand will attract

water and cause corrosion.

Saltiness, CO2 and chloride in the air and humidity along the sea shore will increase the risk of corrosion

of steel bars. Hardening accelerators used in cold winters may cause the same effect. The resulting

calcium-chloride corrodes the steel bars in porous concrete. When the spacers in the concrete

construction are not properly placed, a too thin coverage of the reinforcement bars may be the result

and is followed by corrosion. The corroding (and thus expanding) steel bars will break the outer layer

of concrete away and the stirrups and reinforcement bars will be exposed to more corrosion. At

maximum design loads, the concrete construction may than fail. Kathodic protection may prevent in-

water corrosion. Repair in an early stage is possible. In some cases additional external reinforcement is

applied when replacing the entire construction is relatively costly.

Figure 20.

Photo 321

Prefab

Floor

elements

Corrosion appeared >20 years after the construction,

because of the acceleration additives used during the winter

in the pre-fabrication process during winter.

1 Photo source: https://www.keuringsdienstvoorwonen.nl/nieuws/herken-betonrot-mantavloer-en-kwaaitaalvloer-aan/


https://www.keuringsdienstvoorwonen.nl/nieuws/herken-betonrot-mantavloer-en-kwaaitaalvloer-aan/


19

The most likely cause was that during the prefabrication process during the winter period, hardening

accelerators were used, containing calcium chloride.

Because of high humidity and the calcium chloride, the two

lowest and critical bars corroded, the floors needed

strengthening or replacement all together.

Photo 331. New support under floor.

Repair was in some cased realised by separate bow-string

support structures with tension bolts. Other repair options

included protecting the bars and the pasting of an U profile

over the affected area.

Photo 342 Balcony

Photo 353 Floor

underside

Both are examples

of the poor quality

of concrete or/and

too thin concrete

coverage on the reinforcement bars. By not controlling the small bar supports before casting the fresh

concrete, the reinforcement bars may be laying too close to the formwork (lack of inspection). From

the photo it seems that the reinforcement bars were not lifted during the casting, signifying inadequate

skill of the concrete workers. The loose cut-offs from the binding wire need to be removed before the

concrete floor or beam is cast. When this is not done, they will corrode and cause chipping of the

concrete ceiling, exposing the steel bars and cause further corrosion.

Photo 36. Poor quality formwork.

In this case, many gaps are shown between the planks.

The contractor will often lay the papers from used

cement bags over the floor, before the reinforcement is

placed. At best a sheet of plastic foil is placed over the

plank formwork. Saving on formwork may result in poor

quality concrete. Having a layer of plywood over the used

planking is a better solution.

The above points illustrate that the quality of the concrete can be affected in many different ways.

Even when the engineering calculations are correct and the reinforcement bars are well paced, the

overall quality of the construction can be adversely affected by poor on-site concrete quality. On-site

inspection by qualified inspectors, not from the same contractor, is necessary.

1 Photo source: www.vink-groep.nl/home-betonreparaties 2 Photo source: https://www.verbouwkosten.com/betonrot/ 3 Photo source: www.betonrenovatienederland.nl/betonrot.html/


http://www.vink-groep.nl/home-betonreparaties

https://www.verbouwkosten.com/betonrot/

http://www.betonrenovatienederland.nl/betonrot.html/


20

14. Smooth and Profiled Steel Bars

Reinforced concrete constructions that date from before 1970 commonly have smooth steel

reinforcement bars. These have a lower maximum tensile strength than the cold-deformed and

profiled bars, and have lesser adherence to the concrete than the profiled bars. The effect is

dramatically visible in the aftermath of many earthquakes where older buildings collapsed. When the

maximum design forces were not exceeded due to foundation failure, those collapses are usually

primarily caused by:

➢ poor concrete quality; faulty aggregate mixture, low cement quantity or quality;

➢ improper reinforcement design such as no caging around maximum moment areas, and:

➢ leaving out reinforcement bars, or wrong position of the reinforcement bars,

The first aspect is commonly shown by large amounts of reinforcement steel that is pulled out of the

building debris when the rubble of the collapsed building is being cleared.

Photo 37. Left.

Old type smooth steel

reinforcement bars, recovered

after the earthquake in

Indonesia. These are sold as

scrap iron.

Photo 38.Right

Profiled and stiffer steel reinforcement bars recovered. These are from

buildings constructed in the last 20 years in Kathmandu.

Photo 39.

Recovered complete column reinforcement after the Nepal 2015

earthquake near Kathmandu. These sets of reinforcement can be

used again. There is little wrong about the steel bars. What was

wrong, was the concrete quality, the reason of building failure.

Photo 40. Steel reinforcement bars from schools,

from the 12 May 2008 Sichuan earthquake that

caused over 68,700 deaths.

Researchers tabulated 3500 deaths in only 18 of the

1400 damaged schools. This suggests that many

thousands of students perished in these schools.

However, government data indicated only 7000

student deaths. The contractors (under government

supervision) had largely skipped on cement quantity

for the reinforced concrete. This resulted in fudge-quality concrete. The Ai Weiwei1 art installation is as

a protest against corrupt government controllers and contractors, but most information about the

disaster, corruption and protests have been suppressed by the government.

1 Website: http://artasiapacific.com/Magazine/64/AiWeiweiChallengesChinasGovernmentOverEarthquake and photo: https://www.theguardian.com/artanddesign/2015/jun/15/ai-weiwei-ra-show-sichuan-earthquake-chinese-artist-steel-rods#img-1


http://artasiapacific.com/Magazine/64/AiWeiweiChallengesChinasGovernmentOverEarthquake

https://www.theguardian.com/artanddesign/2015/jun/15/ai-weiwei-ra-show-sichuan-earthquake-chinese-artist-steel-rods#img-1


21

The former paragraphs show that failure of reinforced concrete constructions is not always due to the

architectural and engineering design features, or from design mistakes in the steel reinforcement, but

very often due to the poor concrete quality. There seems to be no systematic collection measurement

data from post-disaster reinforced concrete. Comparisons between the death-toll from poor reinforced

concrete quality, or the death-toll from poor engineering design, is not available.

Inspection and control of the design and its calculations, the formwork on-site, steel BEFORE the casting

of the concrete and most of all the actual concrete quality and the curing method, are crucial in the

overall compliance of the quality standards to which the building should conform.

15. Government or Private Control on the Design and Execution

The massive 7.6 Richter earthquake of 8 October 2005 destroyed all houses in Balakot, and caused heavy damage in Manshera and further districts of the Muzaffarabad region. The depth of this

earthquake was about 25 km, its effects being spread over a 50 km wide area. Over 80,000 people

were killed and over 3 million people were left homeless. The at that time estimated reconstruction cost was over 5,000 million USD.

Photo 41 and photo 42, taken some time later.

The Margalla Towers,

Islamabad.

In Islamabad, 65 km

away from the epicentre, some of the

poorly constructed

apartment buildings,

the Margalla towers, pancaked (photo 42). Collapsing ground floor columns caused half a building to

rip apart (photo 41), collapse and take the next building down with it.

At two and a half time the distance between hypocentre and epicentre1, the impact of the Balakot

earthquake was considerably reduced in Islamabad. Commonly in large towns there is better control

of the building design and execution than in the rural area where this earthquake occurred. In this case no other large multi-storey buildings in Islamabad had serious damage or collapsed. This indicates

that there was something seriously wrong about the government control on the design, the on-site

inspection of the reinforcement, and the concrete quality.

The post-earthquake analysis indicated that most of the 7800 buildings that were damaged were built

without any Seismic Code considerations, mainly because they were realized in the rural areas where no control is exercised over the construction of 1-3 storey dwellings. It was recognised by the Federal

and Provincial State that training of village masons and contractors would be an essential element in

the success of better reconstruction. This is especially so because most houses that will be

reconstructed will be so called non-engineered constructions.

1 At an angle of 45 degrees upwards from the hypocentre (reaching at the earth surface), the horizontal impact of the shockwave may become slower and larger than measured directly from the epicentre. Also the vertical and horizontal impact of the shockwaves will become smaller with the increase of the distance. At 2,5 times the distance, both the vertical and horizontal impact would be less than half of that near the epicentre.



22

After the earthquake the Government started to improve on the existing Seismic Code, but the

implementation requires a massive educational process, especially for all the self-help builders. Also the supply of standard drawings for one-family houses, the expansion of the same, the creation of

municipal controlling entities and the organisation of on-site control mechanisms are required.

In order to train large numbers of masons and concrete workers a cascade system of training was

developed after a team of experts had developed an appropriate curriculum on the subject.

❖ 22 Training Coordinators were developed who became involved in: ❖ training at district level of 150 staff from Housing Reconstruction Centres. These were

organised to become Master Trainers, who became involved in: ❖ training at council level of 650 staff from Partner Organisations to develop Mobile Teams. ❖ The Mobile Training Teams were in charge of the training of artisans, masons, self-help

builders, building contractors, communities, etc. An important task of these different training units was the awareness raising among the population about the possible seismic hazards and the reasons of the extensive building damage. Important in this phase was that it became better understood that earthquakes are recurrent natural phenomena, and that the resulting disasters were man-made due to poor construction habits. These trainings were realised in one-day programmes during which also the Earthquake Reconstruction and Rehabilitation Authority (ERRA) distributed guidelines and posters.

In special programmes attention was given to educate the females because they often supervise house construction when the males are working elsewhere. Radio programmes included answering sessions of questions from the field. Newspapers focussed regularly on the issues and disseminated construction technology. Other media such as exhibitions and school discussions were part of the educational programmes that would lead to awareness raising among the population on better construction techniques.

16. Thin Flat Reinforced Concrete Roofs

After the 24 April 2013 disaster of the collapse of the Savar

building at Rana Plaza complex in Dhaka1, Bangladesh, I was

contacted by another entity about their textile factory. The

roof of their building was sagging substantially.

Figure 21. Thin, flat concrete roof.

Apparently the thin reinforced concrete roof was cast exactly

horizontal, not having a pitch to compensate for initial

sagging or allowing rainwater to discharge to the sides.

After adding the 10 cm insulation layer of cement mortar, 2

cm waterproof plaster and demoulding, the roof sagged

more and rainwater collected in the centre, causing leaks.

1 See: https://en.wikipedia.org/wiki/2013_Savar_building_collapse Quote: “The direct reasons for the building problems

were: (1) Building built on a filled-in pond which compromised structural integrity, (2) Conversion from commercial use to

industrial use, (3) Addition of three floors above the original permit, (4) The use of substandard construction material (which

led to an overload of the building structure aggravated by vibrations due to the generators)”.


https://en.wikipedia.org/wiki/2013_Savar_building_collapse


23

Another layer of 15 of cement mortar and water proofing was added to create rainwater drainage to

the sides. Again the roof beams and floor sagged more and subsequently the imminent danger of

collapse was evident.

Reviewing this other textile factory roof in Dhaka, similar observations can be made as was the case

with the Savar building collapse.

One or more of the following could be possible:

a. Maybe the owner company thought to later add on an extra floor to expand the factory? Little

or no control existed in Dhaka (or corruption was easily possible), being demonstrated with

the collapse of the Savar building. With an extra floor, a pitched roof is not desirable.

b. The use of substandard construction materials, mainly the aggregates and cement (quantity).

When the aggregate composition does not comply with the required density by correct sizing

and quantity of the various aggregate fractions, it may be porous and with that have a lower

compression strength than the design strength. On-site quality control is essential here.

c. In casting a thin reinforced concrete floor, the weight of the fresh concrete will compress (or

settle) the formwork a little. The construction of the formwork should consider this.

d. When the floor and beams will be demoulded (when the concrete has hardened), the beam

and floor will develop their carrying capacity only after elastic flexing (sagging) a little. The

formwork should therefore have a small arch-rise that is at least equal to the calculated flexing

by the full deadweight, including the roof covering (insulation) and waterproofing.

e. When the formwork is largely demoulded, not leaving for one month the central supports

under the beams and floors, additional sagging will occur in the non-fully-hardened concrete.

f. When the top floor in a hot, sunny climate is not constantly watered, the hardening process

may become incomplete, causing weaker concrete than the design requirements; and thus

extra sagging. Creating a layer of standing water on the roof will keep it wet and cool.

g. When the actual roof load is higher than the design load, due to additional cement mortar

layers and waterlogging, the flexion will be larger than calculated.

17. Prefabricated Lightweight Wide-Slab Floors (BubbleDeck)

A large parking garage in Eindhoven airport, The Netherlands, was designed with light-weight and long-

span, very wide-slab (inverted-T-beam) floor elements. These elements are self-supporting during

transport to the construction site and the construction period. A pressure layer is cast on top while

being temporarily supported, to create the desired bearing strength. Smaller sizes of this design are

commonly practised in office and other utility buildings. From the building under construction a roof

section collapsed1, prompting an extensive investigation about the reasons.2

It is very important to investigate the details of a collapse, in order to prevent similar events in the

future and to know if other buildings have safety risks. Following the outcome of that investigation, a

systematic approach of reviewing all similar buildings that were realised in the failed system is than

necessary. Appropriate action should be undertaken if other risks are identified.

1 See with animation video from BAM: https://www.ed.nl/eindhoven/aansluiting-van-betonplaten-en-temperatuur-oorzaak-instorting-parkeergarage-eindhoven-airport~ae3eabcf/ 2 Report with drawings: http://nieuws.eindhovenairport.nl/159245-onderzoeksresultaten-gedeeltelijke-instorting-van-de-in-aanbouw-zijnde-parkeergarage-p1-eindhoven-airport-bekend with links to additional technical reports (PdF)


https://www.ed.nl/eindhoven/aansluiting-van-betonplaten-en-temperatuur-oorzaak-instorting-parkeergarage-eindhoven-airport~ae3eabcf/

https://www.ed.nl/eindhoven/aansluiting-van-betonplaten-en-temperatuur-oorzaak-instorting-parkeergarage-eindhoven-airport~ae3eabcf/

http://nieuws.eindhovenairport.nl/159245-onderzoeksresultaten-gedeeltelijke-instorting-van-de-in-aanbouw-zijnde-parkeergarage-p1-eindhoven-airport-bekend

http://nieuws.eindhovenairport.nl/159245-onderzoeksresultaten-gedeeltelijke-instorting-van-de-in-aanbouw-zijnde-parkeergarage-p1-eindhoven-airport-bekend


24

Photos 43 and 44.

The BubbleDeck

floor is a well-

tested and often

applied system of

light-weight, large

span floor system

for multi-purpose

buildings.

A section of the top floor collapsed and took the lower floors down with it. The causes of the collapse

were extensively investigated and laboratory tests executed the verify the collapse theory.

Figure 22.

The development of a moment.

The sketch shows the connection

between the slabs and the extra

moment that was developed

during the very hot sun.

The resistance to the moment at the location of the joint between the wide-slabs is determined by:

a. The tensile strength of the connecting reinforcement (red in the drawing).

b. The anchorage capacity of all the connecting reinforcement to the concrete (red in the drawing).

c. The resistance to the shear force occurring between the pre-fabricated wide-slab top surface

(being rather smooth) and the cast-on concrete pressure layer (adherence).

d. The floor elements were spanning the shortest span distance of the floor, but with use (net

loading by parking) moments would be developed in both horizontal directions of the floor. The

connecting reinforcement (red in the drawing) is required to meet these forces.

Figure 23. Schematic shear force and moment.

The resume of the investigations was as follows:

a. On the day the top layer was cast, high

sunshine was causing thermal expansion of the

upper side of the pre-cast elements. This

caused the floor to expand and the entire floor

wanting to arch up. This force created a large

shear force between the prefabricated

elements and the cast concrete.

b. Because of the connection with the columns,

the arching-up of the floor is prohibited, this

caused the development of additional moment

forces in the floor.

c. The lack of adherence between the pre-cast wide-slab and the cast-on pressure concrete existed

because the surface of the pre-fabricated elements were smooth and no vertical reinforcement

additions were existing at the location where the additional tension reinforcement was placed.



25

d. The concrete quality of the columns and floor was adequate and not the cause of the failure of

the top floor. Photo’s showed that the reinforcement bars snapped.

e. The lower floors would not have collapsed when the top floor would not have fallen down.

f. The failure of the top floor should not have occurred when: (1) the design of the connection to

the columns would have allowed horizontal (thermal) expansion of the floor; (2) the topside of

the prefabricated slabs was rough for better adherence of the cast-on concrete, including more

vertical reinforcement; (3) the prescribed safety margins (according to the building code) for the

used type of reinforcements would have been applied; (4) the roof of the building would have

had good thermal insulation; (5) municipal controlling entities would have the capability to assess

the applied building systems and execute on-site control of the works.

Although the construction system was proven successful for many utility buildings, in this parking

garage long spans were used for large surfaces, larger than common office buildings. This design

combined large-span floors with low-weight and prefabricated working methods, seeking the borders

of floor engineering and cost efficiency. Because the thermal expansion problem in combination with

the restraining columns and the smooth surface of the wide-slabs were not foreseen (and

subsequently the code’s safety margin for the connecting reinforcement was not applied) the

collapse resulted.

Following the results of the above investigation, the following measurements were taken:

➢ Similar multi-floor building constructions that were realised with this BubbleDeck and similar

light-weight floor systems would be investigated, excluding the shorter span housing and

situations where the wide-slab systems are supported on all four sides.

➢ Building contractors and engineering firms are requested to participate in the investigation,

while municipal entities are involved with the follow-up in case certain risks are identified.

18. Structural Safety Resume

Structural safety is an issue that gets attention when a building collapses, in particular reinforced

concrete constructions. Often with earthquakes the build-in problems, such as design and

construction mistakes, lack of quality control and even corruption come to light.

Three levels can be identified:

❖ At Micro-level: individual mistakes in the design1, execution and on-site control2 of the

buildings by people working in the construction sector. Good work specifications are part of a

good design3.

1 In many countries the architects have inadequate engineering knowledge and make designs that are difficult to realise. Close contact between the engineers and the architect is necessary in those cases, and modification of the design may be a solution that needs approval by the principal. 2 Municipal staff is often over burdened with administrative tasks and have little time to control in detail whether the designs do comply with the building code, or the execution on-site with the designs. The temptation of rubber stamping the designs (without going into the field) is very high for underpaid employees. 3 The detailed designs are also required for future reference or revision of the building. What reinforcement and where the reinforcement is located is of importance when buildings are being modified for different use. In some cases the construction on-site may be altered; in that case the revisions should be indicated on the drawings.



26

Designers do not always adequately specify the materials or construction sequence or detail

special connections1. In these cases the execution depends on the skill2 of the construction

worker or the contractor on how to realise a construction.3

❖ At Meso-level: covering the coordination between the different parties involved in the

building process4. These include the architect, engineer, contractor5, factory, sub-contractor

and the various parties involved in the product approval6, certification7 and on-site

inspection8. In this category also the linkage between the various building actors is

comprised. 9

1In some cases the designers consider that the building inspectors that are responsible for the building permit will verify all the details and will signal any mistakes (not the case). On the other hand, the building inspectors may assume that the designers have done their work correctly and do not re-calculate all the details. 2 By keeping the building costs low, less skilled workers are often employed. By having no idea at all what is required for a good design or construction by these people, more supervision is required at the building site. 3 The case of the sagging roof construction in Bangladesh is a combination of poor design and not giving the floor sufficient arch-rise by the contractor and workers making the formwork. 4 When iron workers (bar benders) are responsible for the correct position of the ironwork, but the contractor is in a hurry, it can happen that the concrete is poured before the bar benders were ready, or the floor was duly inspected by the building inspector (according to the drawings) and given free for the pouring of the concrete. 5 Do all the implementing parties have the latest versions of the drawings? How is the drawing management organised on the building site? 6 Building inspectors who are supposed to give the building permits do not always indicate to the executing party a what elements they should pay special attention in order to avoid mistakes. 7 When a contractor purchases a certified product, he depends om the factory supplying the correct item. The contractor or works inspector will not be able to test the supplied product. In this case the certification process in the factory should be failproof and the factory should supply the requested product and not a lower quality. 8 For large non-standard type of buildings, specialized engineering firms are being contracted to detail the design. The overall complexity of these buildings is often above the ability of the municipal agencies or local building inspectors to verify. The same applies to simple multi-storey buildings in small rural villages or communities. 9 When a prefabricated beam breaks in the building, it could be of poor design, material deficiency, wrong transport, wrong application on site, overload and more. It is not always the mason who is solely responsible.



27

❖ At Macro-level: The building codes1, including seismic codes, safety margins, the legislation

(also as part of the codes), continued responsibility2, the authority3 and enforcement

structure4. The education sector5 and the public information including access to information.

The finance and insurance sector of building6.

Resuming it can be stated that in most cases where building collapse has occurred, one or several

elements of the entire chain between design, building codes, control and construction work were not

correctly managed or executed.

The earthquakes themselves are seldom the reason of collapse or reinforced concrete buildings, but

they do expose the errors made in the past during the design and construction process. In the case of

newer updated seismic codes, the older, long time existing buildings seldom are reviewed and

updated according to the latest knowledge levels.

To educate the entire population about the proper building code is a complex task, requiring action at

multiple levels, including a clear legislative system where individual and mutual responsibilities are

laid down, and adequate sanctions apply when the National Building Code in not applied.

************

1 Generally constructions are supposed to last a minimum of years (e.g. 50 years), however, when those years have gone by, standards may have changed or the quality of the construction cannot be guaranteed anymore. A new assessment should be made to validate the still existing construction against the latest building codes. 2 When the different partners in the entire production chain remain long time responsible for their product, their involvement in quality control and on-site supervision will also improve. That is, when sanctions are strong. The legal chain responsibility must be embedded in the law and insurance systems. 3 Municipal inspectors do not always stop the building process until a mistake has been corrected. Stopping will usually be very expensive for the contractor. Because of these reasons, the building sector is very vulnerable to corruption, and too many construction errors are paid off. 4 When there does not exist a system of sanctions and correction when a mistake is detected, the designer or building contractor has no incentive to improve its performance. When a real estate developer builds mainly to sell the building as fast as possible, that developer has less interest in good quality control as compared to the owner-builder who has to live in the building. 5 Skill among construction workers is mainly developed under guidance of skilled workers and close supervision by inspectors. When there is no time for such guidance or supervision, the educational process becomes poor. 6 When a construction company does not get finance or the building owner cannot obtain a building insurance because the construction quality cannot be guaranteed, they will forcibly have to review the design.


Reinforced Concrete Construction Failures Exposed by ... · public education about seismic risk and...

Documents

Transcript of Reinforced Concrete Construction Failures Exposed by ... · public education about seismic risk and...