Shear Wall Structures

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HIGH RISE STRUCTURAL SYSTEM SHEAR WALLS Group 2 Dhruv Gupta Jeetika Malik Shanu Singh Thangmuangsang Guite

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Explains Building with Shear wall

Transcript of Shear Wall Structures

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HIGH RISE STRUCTURAL SYSTEMSHEAR WALLSGroup 2 Dhruv Gupta Jeetika Malik Shanu Singh Thangmuangsang GuiteINTRODUCTIONA shear wall may consist of : A solid wall. A perforated wall A closed loop or a core. Other such form.

Shear walls are specially designed structural walls included in the buildings to resist horizontal forces that are induced in the plane of the wall due to wind, earthquake and other forces. They are mainly flexural members and usually provided in highrise buildings to avoid the total collapse of the highrise buildings under seismic forces. Shear wall has high in-plane stiffness and strength which can be used to simultaneously resist large horizontal loads and support gravity loads

A shear wall is needed in a bldg.:

1 . To Resist Hor. Loads.

2. To Control Hor. Deflection

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A type of rigid frame construction. The shear wall is in steel or concrete to provide greater lateral rigidity. It is a wall where the entire material of the wall is employed in the resistance of both horizontal and vertical loads. It Is composed of braced panels (or shear panels) to counter the effects of lateral load acting on a structure. Wind & earthquake loads are the most common among the loads. For skyscrapers, as the size of the structure increases, so does the size of the supporting wall. Shear walls tend to be used only in conjunction with other support systems.

SHEAR WALL SYSTEM

Shear walls must provide the necessary lateral strength to resist horizontal earthquake forces. When shear walls are strong enough, they will transfer these horizontal forces to the next element in the load path which may be other shear walls, floors, foundation walls, slabs or footings.

Shear walls also provide lateral stiffness to prevent the roof or floor above from excessive side-sway. When shear walls are stiff enough, they will prevent floor and roof framing members from moving off their supports. Also, buildings that are sufficiently stiff will usually suffer less nonstructural damage.

BASIC FUNCTIONS OF SHEAR WALLOVERALL GEOMETRY OF WALLS Shear walls are oblong in cross-section, i.e., one dimension of the cross-section is much larger than the other. While rectangular cross-section is common, L- and U-shaped sections are also used . Thin-walled hollow RC shafts around the elevator core of buildings also act as shear walls, and should be taken advantage of to resist earthquake forces.

REINFORCEMENT BARS IN RC WALLSSteel reinforcing bars are to be provided in walls in regularly spaced vertical and horizontal grids The vertical and horizontal reinforcement in the wall can be placed in one or two parallel layers called curtains. Horizontal reinforcement needs to be anchored at the ends of walls. The minimum area of reinforcing steel to be provided is 0.0025 times the cross-sectional area, along each of the horizontal and vertical directions. This vertical reinforcement should be distributed uniformly across the wall cross-section.

TYPICAL ARRANGEMENT OF SHEAR WALLS

SUITABLE LOCATIONS :Enclosures around lift wellsStaircase wallsExternal wallsSome of partition walls can be made to act as shear walls.SHEAR WALL: VERTICAL ANALOGY AS CANTILEVER BEAMS

A simple building with shear walls at its ends. Ground motion enters the building and creates inertial forces which move the floor diaphragms. This movement is resisted by the shear walls, and the forces are transmitted back down to the foundation.

TYPES OF SHEARWALL CONSTRUCTION CROSS WALL CONSTRUCTION : A no. of cross and long walls acting both as load bearing walls and shear walls to resist horizontal .loads. MASONRY BUILDINGS :Ht. Range limited to 3-4 storeys due to weakness of masonry in tension. RCC SOLID WALL CONSTRUCTION: Very stiff & very efficient.ADVANTAGES:Very stiff system. Walls can be made act both functional walls as well as structural walls.DISADVANTAGES:Walls must be permanent. Large openings cannot be provided

EXAMPLE: 29 storeyed Hamilton Court Apartment Bldg. at DLF Gurgaon. This bldg. has RCC walls acting as shear walls.

TYPE OF SHEAR WALL SYSTEM SHEAR WALLS ACTING WITH FRAMES :A combination for shear walls and frames or columns.ADVANTAGES :Provide flexibility of planning.Feasibility of providing large spans.Ideal for buildings from 15 to 40 storey ht.Most common form for medium height to high rise buildings,15 to 40 storeyes ht. to be constructed in India in near future.

TYPES OF SHEAR WALLS( based on materials)

RC Shear Wall Plywood Shear Wall Mid ply Shear Wall RC Hollow Concrete Block Masonry Wall Steel Plate Shear WallDESIGNING OF SHEAR WALLS:

Design of shear walls of structures is generally controlled by flexure and overturning rather than shear, especially for wall of a large (ht./length) ratio.Shear walls, when provided, should be continued upto foundations. These should not be discontinued in the lower storeyed.Shear walls should preferably be well distributed about both axes to provide adequate resistance against Torsion.Minimum area of shear reinforcement should be 0.25% x gross sectional area of wall.As horizontal force due to wind or earthquake may act from either direction, shear walls should be provided along both axes to provide resistance along both axes.STRUCTURAL FORMS OF SHEAR WALLSMonolithicshear wallsare classified as short, squat or cantilever according to their height to depth ratio.

Generally shear walls are either plane or flanged in section, while core walls consists of channel sections.

POSITIONING OF SHEAR WALLS

The shape and plan position of the shear wall influences the behavior of the structure considerably. Structurally, the best position for the shear walls is in the centre of each half of the building.This is rarely practical, however, since it dictates the utilization of the space, so they are positioned at the ends.

SHEAR WALL IN HIGH RISEWhen the buildings are tall,, beam and column sizes workout large and reinforcement at the beam and column junction works out quite heavy, so that, there is a lot of congestion at these joints and it is difficult to place and vibrate concrete at these places, which does not contribute to the safety of buildings. These practical difficulties call for introduction of shear walls in highrise buildingsAction to be considered:Shear wall formed around elevator and service risers requires a concentration of opening at ground level where stresses are critical.Torsional and flexural rigidity is affected significantly by the number and the size of opening around the shear walls throughout the height of the building.Shear wall vertical movements will continue throughout the life of the building.Construction time is generally slower than for a steel frame building.The additional weight of the vertical concrete elements as compared to steel will induce a cost penalty for the foundations.An increase in mass will cause a decrease in natural frequency and hence will most likely produce an adverse affect of the acceleration response depending on the frequency range of the building. But shear wall systems are usually stiff and cause a compensating increase in natural frequency.

Example1: Vikas Minar, New Delhi

Office building with a square floor area of28.5 m x 28.5m.Tube in tube structure with shear walls acting as core.Height:82.3 mtsNo. of storeys: 23

KEY PLANTYPICAL FLOOR PLAN Example 2: Al Sharq Tower,DubaiThe core has reinforced concrete shear walls that extend out to the perimeter between each cable-wrapped tube. This extensive structural support is what allows the tower's height on such a small footprint.The tubes taper as the shear walls between them get thicker at the building's base, and the cables are gathered and attached in groups to the building's foundation.The 1,180-foot Al Sharq tower has a sleek 1:10 aspect ratio (the Sears tower, for example, has a ratio of 1:5), which is achieved by gathering nine 40-foot-diameter tubes (each with a 1:30 aspect ratio) into a cell-like matrix. The center tube is a concrete core, with reinforced shear walls that are 50 inches thick at the base and taper to 23 inches thick at the upper levels. The shear walls extend slightly from the core to serve as support between each of the eight perimeter tubes

Example 3: Office Building, TehranThe tower is a 56-story tall building, located in Tehran, which is the most high seismicity zone of IranThe tower has three transverse main walls with the angle of 120 and multiple sidewalls perpendicular to each of them .It seems that this kind of architectural configuration is due to aesthetic considerations. Structural system Main walls are RC shear walls with regular staggered openings. Sidewalls are also RC shear walls, connected to the main walls with coupling beams. Some of sidewalls contain continuous column of openings and the rest are solid.

Example 4: OfficBurj KhalifaProject NameThe Burj TowerDuration47Months (Feb. 05 ~ Dec. 08)Cost876,000,000 USDOwnerEMAAR PropertiesFloorsAbove 160 floorsHeightAbove 800mUsageHotel, Residence, Office

Hotel (L39)Residence (L108)SpireObservatory (L123)Communication (L160)Office (L153)PinnacleGross area tower : 279,000 sq. MGross area podium : 186,000 sq. MTotal concrete quantity tower : 145,000 cubic MTotal concrete quantity podium : 115,000 cubic MOverall concrete quantity : 260,000 cubic MOverall rebar quantity : 34,000 tonsStructural OverviewY-shaped floor plan is ideal for residential program Maximizes window perimeter to floor plate areaIs inherently stable

Buttressed coreThree wings arranged around central coreEach wing supports other two

Setbacks occur at each wing in a spiraling pattern Reduces vortex shedding by changing building shape 24 times

The structure of Burj Khalifa was designed to behave like a giant column with cross sectional shape that is a reflection of the building massing and profileTypical Floor Plan

Hotel Residential Floor plan

Floor Framing PlansTypical Hotel LevelTypical Mechanical LevelLocationElevation Drift (m) (mm)

Top Communications +604.91450

Top Office +569.71250

Observatory +442.1 750

Top Residential +375.3 540

50 year wind event

Predicted Wind Drift3D View Under Construction

Structural OverviewConcrete Placement

CPB#1CPB#3CPB#4CPB#2LevelHeightPouring MethodRemarksGround ~ L145531 mDirect PumpingTarget Height (RC Structure)L146 ~ L160M624 mRe-pumpingSecondary Pump on L124 (East wing 442m)L160M ~ Spire1681.7 mHopper by T/CFrom Ground LevelLevelPressureOutputEngineRemarksPump#1~#3185 / 320 bar71 / 36 m3/hr470 kw2 nos. of Main1 no. of Stand byPump#4220 / 260 bar110 m3/hr200 kwSecondaryPumpingPumping Area (Ground Level)Pipe LinesConcrete Pump. Pipe Lines

D150mm, THK 11mm 5 Lines (1 for back up). Concrete Placing Boom

32m boom for Center Core 3nos. of 28m boom for Wing Core

Construction Photographs