Modular Steel Girder Design for 40 m, 50 m and 60 m of Span in

Indonesia

By

Sudahraa), Febry Pernatab)

Synopsis

Indonesia is an archipelagic country with large population. There is about 17,500 of islands and

261 million of population. Even though Indonesia is a large country, the population is concentrated

in few regions. Geographical conditions and patterns of population distribution require the

development of appropriate infrastructure such as bridges to connect between islands and elevated

highway or flyovers to overcome land constrains. Currently steel structure is more popularly used

for girder on bridge and elevated highway. Some of advantages on steel compared to concrete base

are faster in fabrication and assembling, high quality cost but optimally distributed for the large

number of spans, as well as better term for aesthetic.

This paper describes in brief the experiences of PT Krakatau Steel (PTKS) in designing of modular

steel girder for 40 m, 50 m and 60 m of span. PTKS is assisted by PT. LAPI ITB as a independent

consultant in term to get prime and appropriate design for the girder. The design purposely

considers the local steel optimization. The steel girder dimensions and properties are designed to

utilize steel plate from PTKS and Local Steel Companies with 450 – 550 Mpa of yield strength,

20 – 24% of elongation, 1,700 – 2,500 mm of width and 20 – 22 mm of thickness. The design

method and calculations are based on regulations and standard that apply in Indonesia. Analysis

and calculation focused on the steel girder while pier, pierhead and foundation will adjust to the

topography, soil type and seismic parameters of the location. Additionally, the production cost

becomes lower so that be overall cost of the girder or even the project becomes more competitive.

The PTKS steel girder design expected to be default design for development of bridges and

elevated highway or flyovers in Indonesia. So that the constructions are faster, high quality, low

budget and better aesthetic. Besides, the role of local steel companies will be more optimal.

Keywords: Modular Steel Girder, 450 – 550 Mpa of yield strength, 1,700 – 2,500 mm of width

a) Engineer of Technology Development, PT Krakatau Steel (Persero) Tbk b) Senior Engineer of Mechanical & Civil Engineering, PT Krakatau Steel (Persero) Tbk

I. INTRODUCTION

Infrastructure development play important role to accelerate economic growth. Indonesia

is an archipelagic country with large population. However, the population is concentrated in few

regions. Geographical conditions and patterns of population distribution of Indonesia require the

development of appropriate infrastructure such as bridges to connect between islands and elevated

highway or flyovers to overcome land constrains. PT Krakatau Steel has responsibility to support

the development of the infrastructure in accordance with its competence as steel provider.

Currently in infrastructure development, steel structure is popular and play important role

to achieve efficient structure by time and cost. For bridges and elevated highway, the girder can

replaced by steel structure for concrete structure. Some of the reasons are faster in fabrication and

assembling, high quality cost but optimally distributed for the large number of spans, as well as

better term for aesthetic. But for reason of local steel optimization, the design of steel girder should

be meet with capability of local steel companies.

In order to get appropriate girder design which can overcome static and dynamic loads

according to Indonesia base condition and also to accommodate local steel, there two parameters

can be adjusted. They are the dimension of the steel girder and properties of the steel.

II. STEEL GIRDER

Girder is part of upper structure on bridge or elevated highway that serves to channel loads

such as vehicle load, the weight of the girder itself and the other loads above the girder to the lower

part of the structure. Generally, the girder can be in form of profile beam I (I-Girder), Box (Box

Girder) and other shapes that designed as needed. There are five form of girder that are widely

used today, they are I-Girder, Box Girder, U-Girder, T-Girder and Plate Girder.

(a) I-Girder (b) Box Girder (c) U-Girder

(d) T-Girder (e) Plate Girder

Figure 1: Shapes of Girder

All forms of girder can be made of steel or concrete. But for short span it is not

recommended to use steel girders because of the initial high cost.

Currently, the use of steel structures for girders has been very popular. Demands to

produce strong structures at lower costs and faster have led to many innovations related to

construction such as steel girder. There are several advantages of steel girder when compared to

concrete girders such as table 1.

Table 1. Advantages of Steel Girder

Point of

comparation Steel Girder

Concrete

Girder Effect Benefit

Strength to

weight ratio

High Low - good resist of

static load

- longer span

- easier to handling

- low requirement of

foundation

Low cost in total

material,

transportation

and handling.

Formability High Low - faster in

construction

- easier to joint

- more aesthetic

Saving in time

for construction

and assembling

Scrap value Yes No can be recycled Green structure

Ductility High Low - no sudden failure

- can withstand

earthquake more

effectively

- more safe

III. PLAT STEEL PROVIDER IN INDONESIA

Indonesia is one of the largest steel producing countries in Southeast Asia. based on data from

SEAISI in 2018, in 2017 Indonesia was ranked as the 2nd ranked producer of steel in Southeast

Asia with steel production growth of 19.5%. While the first rank of steel producer in Southeast

Asia is Vietnam, which recorded substantial steel production growth 30.5%. Here are the 6 major

steel producing countries in Southeast Asia.

Table 2. Six largest Southeast Asian steel producing countries

Country 2016

Production (tons)

2017

Production (tons)

2017

Portion (%)

Growth

y-o-y (%)

Indonesia 6.582.234 7.866.362 22,7% 19.5%

Malaysia 3.781.668 3.772.057 10,9% -0,3%

Philippines 4.346.038 4.300.249 12,4% -1,1%

Singapore 528.453 595.522 1,7% 12,7%

Thailand 7.977.590 6.875.446 19,8% -13,8%

Vietnam 8.657.000 11.302.000 32,6% 30,6%

ASEAN – 6 Total 31.872.983 34.711.636 100% 8,9%

Development & infrastructure projects that are in line with the policies of the Government of

Indonesia play an important role in the growth of the steel industry in Indonesia for the last 3-5

years. This is evidenced by the increasing budget for infrastructure projects as shown in the

following figure.

Figure 1. Indonesia Infrastructure Budget

In Indonesia there are several steel companies that produce plates as raw material for steel girder,

here are some companies that produce steel plates:

Table 3. Indonesia Steel Plate Provider

Company Work/Location Product

Thickness (mm)

Product

Width (mm)

PT Krakatau Steel Cilegon, West Java 1,2 - 25 600 - 2250

PT Krakatau Posco Cilegon, West Java 6,0 - 120 1200 - 4650

PT Gunung Bekasi, West Java 5,0 – 150 1200 - 3550

PT Jayapari Steel Surabaya, East Java 8,0 – 25 900 – 1550

PT Gunawan Surabaya, East Java 6,0 – 80 1200 - 2500

IV. STEEL GIRDER DESIGN FOR 40 M, 50 M AND 60 M

The design method and calculations are based on regulations and standard that apply in Indonesia.

Analysis and calculation focused on the steel girder while pier, pierhead and foundation will adjust

to the topography, soil type and seismic parameters of the location.

4.1 Structure System

Top structure system of modular bridge or high way is simple span of steel girder structure with

the following information:

a. Girder profile : Composite U Girder

b. Span (L) : 40, 50 and 60 meters

c. Height of girder : 1.7 m (L=40 m) ; 2 m (L=50 m) ; 2.5 m (L=60 m)

d. Width of Girder : 2,0 meters

0%

5%

10%

15%

20%

0

100

200

300

400

500

2013 2014 2015 2016 2017

TrilionRupiah

Infrastructure Budget % of total Budget

e. Number of girder : 3 Girder

f. Number of lines : 3 lines * 3.5 meters

g. Design for vehicle : Truck 50 tons

Figure 2. Dimension of Modular bridge Cross Section in mm

4.2 Standard and Code References

This bridge structure system will be analyzed based on several standards and codes that apply in

Indonesia and other standards are as follows:

a. SNI 1725 – 2016 : Peraturan Pembebanan untuk Jembatan

b. RSNI T03 – 2005 : Peraturan Baja untuk Jembatan

c. RSNI 03 – 2833 – 201x : Perancanagan Jembatan terhadap Beban Gempa

d. AISC Steel Design LRFD

e. AAHTO LRFD Bridge Design Specifications 6th Ed-2012

4.3 Specification of Steel Material

Specification of material that used for the girder and accessories as follows:

a. Steel for U Girder

Grade : JIS G 3106 SM570

Yield Strength : 450 – 540 Mpa

Young Modulus : 200,000 Mpa

Coef. Expansion : 1.20e – 0.5 per Celsius degree

Poisson Ratio : 0.3

Specific Weight : 7850 kg/m3

Elongation : 20 – 24%

b. Steel for Diaphragm and Stiffener

Grade : JIS G 3106 SM520 B

Yield Strength : 355 – 520 Mpa

Young Modulus : 200,000 Mpa

Coef. Expansion : 1.20e – 0.5 per Celsius degree

Poisson Ratio : 0.3

Specific Weight : 7850 kg/m3

4.4 Type of Load

In general, the loading criteria that used in design is consider and reviewed by condition as follows:

Working load/Service load

Working load/service load is load that works during bridge service conditions, this is

related with bridge serviceability.

Ultimate load

Ultimate load is load that obtained from multiply the work load by load factor.

Plan load in this design are categorized to be 2 categories namely permanent load and transient

load. The following is categorization for loads that applied for this design:

1. Permanent Load:

Symbol Description

MS Load of structural and nonstructural bridge component

MA Pavement and utility dead load

TA Horizontal lateral load of soil

PL Forces on bridge structure that occurred by implementation process

PR prestress

2. Transient Load:

Symbol Description Symbol Description

SH Force due to shrinkage TP Pedestrian load

TB Force due to brakes SE Load due to decline

TR Centrifugal force ET Force due to temperature gradient

TC Force due to vehicle collisions EUn Force due to uniformity of temperature

TV Force due to ship collisions EF Buoyant force

EQ Earthquake force EWs Wind load on the structure

BF Friction force EWl Wind load on the vehicle

TD Lane load “D” EU Stream and drift load

TT Truck load “T”

A combination of SNI 1725 2016 factored loading for service life and ultimate conditions are as

table 4.

Table 4. Load combination of SNI 1725 2016

4.5 Bridge Structure Modeling and Analysis

a. Bridge Structure Modeling

Modeling and analysis for main bridge are simulated by MIDAS Civil. Bridge modeling

presented as overall of top bridge structure that consist of girder, pierhead, and pier. All

component modeled as beam element/frame but girder modeled as special beam element

which have composite section. Placement of box girder on pierhead is modeled as boundary

condition rigid link which one end of rigid link is set as hinge and the other one is set as

roller so can represent simple span on girder.

Figure 3. Modeling of Bridge Structure

b. Girder Shape

The steel girder is designed as U-Type girder as shown as follows:

Figure 5. Shape of Steel Girder

c. Bridge Structure Analysis

After modeling the bridge structure and input the loads, the next step is to analyze the

structure by calculations and computer program (MIDAS Civil) to get structure response

in the form of internal force such as axial, shear, and moment of force. The following are

the simulation result with the MIDAS Civil for span 60 m:

Post Construction Stage:

Figure 6. Diagram of moment, summation final stage

Condition due to a combination of strength loads enveloped (kuat I, II, III, IV, V):

Figure 7. Diagram of Moment My, Enveloped strength combination

Figure 8. Diagram of Moment Mz, Enveloped strength combination

Condition due to a combination of extreme loads envelope (extreme I, II):

Figure 9. Diagram of Moment My, Extreme envelope combination

Figure 10. Diagram of moment Mz, extreme envelope combination

V. CONCLUSION OF DESIGN

Modular bridge calculations and analyze have been carried out in accordance with applicable

structural design and loading rules. The following are conclusion of steel U girder design for

composite bridge modular:

Steel grade is SM 570 or 450 – 550 Mpa of yield strength, 20 – 24% of elongation with dimension

of girder:

1. Steel U Girder for modular bridge 40 m of span

2. Steel U Girder for modular bridge 50 m of span

3. Steel U Girder for modular bridge 60 m of span

Reference

1. LAPI ITB & Krakatau Steel, Desain Struktur Jembatan Modular Span 40, 50 dan 60

m,Dok. Krakatau Steel, Indonesia 2017

2. Faqih Ma’arif, M.Eng., Analisis Struktur Jembatan, Learning Module, University of

Negeri Yogyakarta, Indonesia, 2012.

3. Civildigital.com, Complete Comparison of Steel and Concrete, 2018.

4. Badan Standardisasi Nasional, Pembebanan untuk Jembatan, SNI 1725:2016, Indonesia,

2016.