Structural system of Buildings(sub-structure+ super structure)

Structural system of Buildings(sub-structure+ super structure)

1. Structural system of Building Presenting by- 156025 160005 166010 166012 166013 166028 Dept. of Architecture,DUET 1

2. Foundation: Foundation is one of the essential parts of the structure. It is defined as that part of the structure that transfers the load from the structure constructed on it as well as its weight over a large area of soil in such a way that the amount does not exceed the ultimate bearing capacity of the soil and the settlement of the whole structure remains within a tolerable limit. Foundation is the part of a structure on which the building stands. The solid ground on which it rests is known as foundation bed. Substructure: The  substructure  is the part of the building that is underneath the ground, while the superstructure is everything that is above ground.  Substructure . The purpose of the  substructure  of a building is to transfer the loads of the superstructure to the soil that is underneath 2 There are two structural parts of a building: Sub-Structure Super-Structure SUB-STRUCTURE Source:Building constraction illustrated,Francis D.K.Ching (4 th edition) page no:80

3. Why a Foundation is Provided? Foundation should fulfil the following objectives: Distribute the weight of the structure over a large area of soil. Avoid unequal settlement. Prevent the lateral movement of the structure. Increase structural stability. Why There are Different Types As we know that there are different types of soil, and the bearing capacity of the soil is different for each type of soil. Depending on the soil profile, size, and load of the structure, engineers chose different kinds of foundation. 3 SUB-STRUCTURE Source : https://civiltoday.com

4. Types of Foundation In general, all foundations are divided into two categories, - shallow and deep foundations. The terms Shallow and Deep Foundation refer to the depth of the soil at which it is placed. Generally, if the width of the foundation is greater than the depth, it is labelled as the “Shallow Foundation”. If the width is smaller than the depth of the foundation it is called as “Deep Foundation.” However, deep foundation and shallow foundation can be classified as shown in the following chart. 4 SUB-STRUCTURE Source : https://civiltoday.com

5. Shallow Foundations As the shallow foundation depth is low and it is economical, it is the most popular type of foundation for lightweight structures. Several types of shallow foundations are discussed below. 1. Isolated Spread Footing This is the most widely recognized and most straightforward shallow foundation type, as this is the most economical type. They are typically utilized for shallow establishments to convey and spread concentrated burdens caused, for instance, by pillars or columns. They are generally used for ordinary buildings (Typically up to five stories). 5 SUB-STRUCTURE Source:Building constraction illustrated,Francis D.K.Ching (4 th edition) page no:87

6. The followings are the types of spread footing. 6 SUB-STRUCTURE Source : https://civiltoday.com

7. 2. Wall Footing or Strip footing Wall footing is also known as continuous footing. This type is used to distribute loads of structural or non- structural load-bearing walls to the ground in such a way that the load-bearing limit of the soil isn't outperformed. It runs along the direction of the wall. The width of the wall foundation is usually 2-3 times the width of the wall. The wall footing is a continuous slab strip along the length of the wall. Stone, brick, reinforced concrete, etc. are used for the construction of wall foundations. On account of block walls, the footing comprises a few courses of bricks, the least course being generally double the expansiveness of the wall above. On account of stone masonry walls, the counterbalances could be 15 cm, with the statues of the course as 30 cm. Along these lines, the size of footings is marginally more than that of the block divider footings. If the heap on the wall is substantial or the soil is of low bearing limit, this reinforced concrete foundation type can be given. Wall footing is economical when: Loads to be transmitted are of small magnitude. It is placed on dense sand and gravel. 7 SUB-STRUCTURE Source:Building constraction illustrated,Francis D.K.Ching (4 th edition) page no:87

8. 3. Combined Footing The combined footing is very similar to the isolated footing. When the columns of the structure are carefully placed, or the bearing capacity of the soil is low and their footing overlap each other, combined footing is provided. It is fundamentally a blend of different footings, which uses the properties of various balances in a single footing dependent on the necessity of the structure. Combined foundations are economic when: The columns are placed close to each other. When the column is close to the property line and the isolated footing would cross the property line or become eccentric. Dimensions of one side of the footing are restricted to some lower value. The foundations which are made common to more than one column are called  combined footings . There are different types of combined footing, including slab type, slab and beam type, rectangular, raft, and strap beam type. They may be square, tee-shaped, or trapezoidal. The main objective is the uniform distribution of loads under the entire area of footing, for this is necessary to coincide with the center of gravity of the footing area with the centre of gravity of the total loads. 8 SUB-STRUCTURE Source:Building constraction illustrated,Francis D.K.Ching (4 th edition) page no:87

9. 4. Cantilever or Strap Footing Strap footings are similar to combined footings. Reasons for considering or choosing strap footing are identical to the combined one. In  strap footing , the foundation under the columns is built individually and connected by a strap beam. Generally, when the edge of the footing cannot be extended beyond the property line, the exterior footing is connected by a strap beam with interior footing. 9 SUB-STRUCTURE Source:Building constraction illustrated,Francis D.K.Ching (4 th edition) page no:87

10. 5. Raft or Mat Foundation Raft or Mat foundations  are used where other shallow or pile foundations are not suitable. It is also recommended in situations where the bearing capacity of the soil is inadequate, the load of the structure is to be distributed over a large area or structure is subjected continuously to shocks or jerks. Raft or Mat foundations are economic when: The soil is weak and the load has to be spread over a large area. The structure includes a basement. Columns are closely placed. Other kinds of foundations are not feasible. Differential settlement is to be prevented. Raft or Mat foundations   consists of a reinforced concrete slab or T-beam slab placed over the entire area of the structure. In this type, the whole basement floor slab acts as the foundation. The total load of the structure is spread evenly over the entire area of the structure. This is called raft because, in this case, the building seems like a vessel that floats on a sea of soil. 10 SUB-STRUCTURE Source : https://civiltoday.com

11. Pile Foundation: Pile foundation, a kind of deep foundation, is actually a slender column or long cylinder made of materials such as concrete or steel which are used to support the structure and transfer the load at desired depth either by end bearing or skin friction. Types of Pile Foundation Pile foundations can be classified based on function, materials and installation process, etc. Followings are the types of pile foundation used in construction: A. Based on Function or Use 1. Sheet Piles 2. Load Bearing Piles 3. End bearing Piles 4. Friction Piles 5. Soil Compactor Piles 11 SUB-STRUCTURE B. Based on Materials and Construction Method 1. Timber Piles 2. Concrete Piles 3. Steel Piles 4. Composite Piles Source:Building constraction illustrated,Francis D.K.Ching (4 th edition) page no:102

12. The following diagram is representing pile foundation types discussed above. 12 SUB-STRUCTURE Source : https://civiltoday.com

13. Classification of Pile Foundation Based on Function or Use Sheet Piles This type of pile is mostly used to provide lateral support. Usually, they resist lateral pressure from loose soil, the flow of water, etc. They are usually used for cofferdams, trench sheeting, shore protection, etc. They are not used for providing vertical support to the structure. They are usually used to serve the following purpose Construction of retaining walls. Protection from river bank erosion. Retain the loose soil around foundation trenches. For isolation of foundation from adjacent soils. Figure: sheet Pile 13 SUB-STRUCTURE Source : https://civiltoday.com

14. Load Bearing Piles This type of pile foundation is mainly used to transfer the vertical loads from the structure to the soil. These foundations transmit loads through the soil with poor supporting property onto a layer which is capable of bearing the load. In this type of pile, the loads pass through the lower tip of the pile. The bottom end of the pile rests on a strong layer of soil or rock. Usually, the pile rests at a transition layer of a weak and strong slayer. As a result, the pile acts as a column and safely transfers the load to the strong layer. End Bearing Piles Friction Pile Friction pile transfers the load from the structure to the soil by the frictional force between the surface of the pile and the soil surrounding the pile such as stiff clay, sandy soil, etc. In friction pile, generally, the entire surface of the pile works to transfer the loads from the structure to the soil. 14 SUB-STRUCTURE Source:Building constraction illustrated,Francis D.K.Ching (4 th edition) page no:103

15. Soil Compactor Piles Sometimes piles are driven at placed closed intervals to increase the bearing capacity of soil by compacting. Classification of Piles Based on Materials and Construction Method On the basis of materials of pile construction and their installation process load-bearing piles can be classified as follows: 1. Timber Piles i . Untreated ii. Treated with Preservative 2. Concrete Piles i . Pre-cast Piles ii. Cast-in-pace Piles 3. Steel Piles i . I-Section Piles ii. Hollow Piles 4. Composite Piles 15 SUB-STRUCTURE Source : https://civiltoday.com

16. Timber Piles Timber piles are placed under the water level. They last for approximately about 30 years. They can be rectangular or circular in shape. Their diameter or size can vary from 12 to 16 inches. The length of the pile is usually 20 times of the top width. They are usually designed for 15 to 20 tons. Additional strength can be obtained by bolting fish plates to the side of the piles. Advantages of Timber Piles- Timber piles of regular size are available. Economical. Easy to install. Low possibility of damage. Timber piles can be cut off at any desired length after they are installed.  If necessary, timber piles can be easily pulled out. Disadvantages of Timber Piles- Piles of longer lengths are not always available. It is difficult to obtain straight piles if the length is short. It is difficult to drive the pile if the soil strata are very hard. Spicing of timber pile is difficult. Timber or wooden piles are not suitable to be used as end-bearing piles. Figure: timber Pile 16 SUB-STRUCTURE Source : https://civiltoday.com

17. Concrete Piles The precast concrete pile is cast in pile bed in the horizontal form if they are rectangular in shape. Usually, circular piles are cast in vertical forms. Precast piles are usually reinforced with steel to prevent breakage during its mobilization from casting bed to the location of the foundation. After the piles are cast, curing has to be performed as per specification. Generally curing period for pre-cast piles is 21 to 28 days. Pre-cast Concrete Pile Cast-in-Place Concrete Piles This type of pile is constructed by boring of soil up to the desired depth and then, depositing freshly mixed concrete in that place and letting it cure there. This type of pile is constructed either by driving a metallic shell to the ground and filling it with concrete and leave the shell with the concrete or the shell is pulled out while concrete is poured. Figure: Pre-cast Concrete Pile Figure: cast-in-situ Concrete Pile 17 SUB-STRUCTURE Source : https://civiltoday.com

18. Steel Piles Steel piles may be of I-section or hollow pipe. They are filled with concrete. The size may vary from 10 inches to 24 inches in diameter and thickness is usually ¾ inches. Because of the small sectional area, the piles are easy to drive. They are mostly used as end-bearing piles. Combination of different materials in the same of pile. As indicated earlier, part of a timber pile which is installed above ground water could be vulnerable to insect attack and decay. To avoid this, concrete or steel pile is used above the ground water level, whilst wood pile is installed under the ground water level Composite Piles Figure: composite pile 18 SUB-STRUCTURE Source : https://civiltoday.com

19. Classification of pile foundation based on the effect of soil Driven piles Bored piles Screw pile Timber piles Steel piles Driven piles, also known as displacement piles, are a commonly-used form of building foundation that provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics. Driven piles are commonly used to support buildings, tanks, towers, walls and bridges, and can be the most cost-effective deep foundation solution. 1. Driven piles 2. Screw pile Screw pile foundations are a type of pile foundation with a helix near the pile toe so that the piles can be screwed into the ground. The process and concept is similar to screwing into wood. A screw pile may have more than one helix (also called a screw), depending on the usage and the ground conditions. Generally, more helices are specified if a higher load is required or softer ground is encountered. Figure: driven pile Figure: screw pile 19 SUB-STRUCTURE Source : https://civiltoday.com

20. Pier Foundation Pier is an underground structure that transmits a more massive load, which cannot be carried by shallow foundations. It is usually shallower than piles. The pier foundation is generally utilized in multi-story structures. Since the base region is determined by the plan strategy for the regular establishment, the single pier load test is wiped out. Along these lines, it is increasingly well known under tight conditions. Pier foundation is a cylindrical structural member that transfer heavy load from superstructure to the soil by end bearing. Unlike piles, it can only transfer load by bearing and by not skin friction. Figure: Pier Foundation  Caisson Foundation Caisson foundation is a watertight retaining structure used as a bridge pier, construction of the dam, etc. It is generally used in structures that require foundation beneath a river or similar water bodies. The reason for choosing the caisson is that it can be floated to the desired location and then sunk into place Figure: caisson Foundation 20 SUB-STRUCTURE Source : https://civiltoday.com

21. Caisson foundation is a ready-made hollow cylinder depressed into the soil up to the desired level and then filled with concrete, which ultimately converts to a foundation. It is mostly used as bridge piers. Caissons are sensitive to construction procedures and lack construction expertise. There are several types of caisson foundations. Box Caissons. Floating Caissons. Pneumatic Caissons. Open Caissons. Sheeted Caissons. Excavated Caissons. 21 SUB-STRUCTURE

22. 22 TYPES OF SUPER – STRUCTURAL SYSTEMS: SUPER-STRUCTURE

23. POST SLAB A reinforced concrete slab supported directly by concrete columns without the use of beams. Theoretically there is no limit on maximum length. But practically and economically they are restricted. Flat slab without drop and column capital COLUMN SLAB Slab depth: 5’’ to 12’’ Rule of Thumb: For slab depth: Span/33 Suitable for light live to moderate loads over relatively short spans pf 12’ to 24’. Characteristics : Simplicity of forming. Lower floor to floor heights. Span:20’ to 40’ Span 23 SUPER-STRUCTURE Sources:(book name- building construction illustrated, 4 th edition) Page nO:108

24. Flat slab with column capital Fig :Flat Slab With Drop Panel Sources:(book name- building construction illustrated, 4 th edition) Page nO:108 COLUMN COLUMN CAPITAL SLAB Flat slab with drop panel and column capital COLUMN SLAB COLUMN CAPITAL DROP PANEL COLUMN SLAB DROP PANEL Slab: Slab depth:6’’ to 12’’ Rule of Thumb: for slab depth : Span/36 Drop panel: Minimum projection of drop panel =0.25x slab thickness Width:0.33x Span Used :resistance to punching shear. 24 SUPER-STRUCTURE

25. Uses Of  Post Slab Post slabs are mostly used in large industrial structures, parking garages, ramps, warehouse, high rise buildings. They are also used where uses of beams are not required. Major components of flat slab are capital/head, drop panel, columns strip and middle strips. Slab Thickness: Slab without drop panel :125mm Slab with drop panel :100mm 25 STRUCTURAL ADVANTAGES OF FLAT SLAB Economic Faster construction Prefabricated in standard sizes Minimized installation time Better quality control STRUCTURAL DISADVANTAGES OF FLAT SLAB Seismic loading is poor Flat slab failure in earthquake Punching shear punching limitation Cheek shear diagram Each floor should have cantilever. Can not punch at column strip. Sources:(book name- building construction illustrated, 4 th edition) & FLAT SLAB DESIGN BY O’ROUOKE, CE AND SAMUEL BAKER, CE(Serial-2754-4), BNBC 2014, (6.5.2.5)

26. Slab Supported on wall There is no column & beam Wall Slab Load Distribution System Wall slab structure Source:Building constraction illustrated,Francis D.K.Ching (4 th edition) page no:64 26 SUPER-STRUCTURE

27. TYPE OF SLAB BASED ON SUPPORT CONDITION: One Way Slab Two Way Slab Slabs supported on Two Opposite side rectangular in shape. Main reinforcement is provided in short span and distribution reinforcement is provided in a longer span. Slab thickness is more as compared to the two-way slab. Chajja and Varandha are practical example. Slabs supported on four sides. Preferred if the shape of slab is close to square. Effective for medium span and heavy loads. Used in constructive floors of the building. Waffle slab L b L b L/b>=2 L/b<2 Source:Building constraction illustrated,Francis D.K.Ching (4 th edition) page no:64 27 SUPER-STRUCTURE

28. Rule of thumb for estimating thickness: Floor slab : Span/30 (4’’ minimum) Roof slab: Span/36 Suitable for light to moderate loads over relatively short spans of 6’ to 18’. Source:Building constraction illustrated,Francis D.K.Ching (4 th edition) page no:106,107 One Way Slab Two Way Slab Rule of thumb for estimating thickness: Slab depth : Span perimeter/180 (4’’ minimum) Suitable for carrying intermediate loads over 15’ to 40’ span. SLAB THICKNESS & SPAN 28 SUPER-STRUCTURE

29. To control deflection , ACI Code 9.5.2.1 specifies minimum thickness Type of one -way slab Structural depth Diagram Simple supported L/20 One end continuous L/24 Both ends continuous L/28 Cantilever L/10 Position of Stair Wall Support Wall Support t=Thickness of slab Landing ` Landing should be supported by load bearing wall The wall in both sides is the main structural member Parallel walls on two sides can also provide support One-way slab depth: 29 SUPER-STRUCTURE

30. Masonry Wall : Masonry is the most durable part of any structure. It allows for unlimited architectural expressions. They provide strength durability. Masonry wall also helps to control the temperature in indoor and out. Also, it increases the fire resistance. Lateral stiffness of the masonry wall is very low. Engineering Brick Wall : It uses double open-ended bond beam blocks. It is built using a mold . Block wall is replaced horizontally.  Stone Wall : It is treated as a stone structure. It is kind a masonry construction. This wall provides structure to a building and encloses an area. Types of Load Bearing Walls Followings are the types of load bearing walls: Precast Concrete Wall : This wall is aesthetically pleasing. The precast   wall  has superior strength and known for its durability. It provides excellent protection and is easy to install. 30 SUPER-STRUCTURE

31. MINIMUM THICKNESS OF MASONARY WALL: TYPES OF Load bearing masonry wall Min. thickness Stone Masonry Wall 16inch Cavity wall masonry Wall 8inch Hollow unit Masonry Wall 8inch Solid Masonry 8inch Grouted Masonry Wall 6inch Reinforced masonry Wall 6inch Exterior non-bearing walls may be 4’’ less than required for bearing wall , but not less than 8’’ thick, except where 6’’ walls are permitted in residences. Plain (unreinforced)masonry bearing walls must be at least 12’’ thick for the uppermost 35’ of the wall and increase 4’’ in thickness for each successive 35’downward from the top. For buildings not more than 3 stories or 35’ in height, masonry walls may ne 8’’ thick. One- story solid masonry walls not more than 9’’ high may be 6’’ thick. Plain Masonry Bearing Wall Note: Local building codes to verify the structural requirements for masonry. Source:Building constraction illustrated,Francis D.K.Ching (2 th edition) page no:131 31 SUPER-STRUCTURE

32. MINIMUM THICKNESS OF WALLS IN HIGH WIND REGION: Type of Wall Minimum thickness (mm) Unreinforced grouted brick wall 250 Reinforced exterior bearing wall 200 Unreinforced hollow and solid masonry wall 200 Interior non-bearing wall 150 Source:Bangladesh National Building Code-2012(chapter:7)7.4.6 page no6-382,:6-400 The maximum unsupported height of bearing walls or other masonry walls shall be 3.5 m. Minimum Thickness of Load Bearing Walls:  The nominal thickness of masonry bearing walls in building shall not be less than 250 mm.     Exception:   Stiffened solid masonry bearing walls in one‐story buildings may have a minimum effective thickness of165 mm when not  over 3 m in height,  provided that when gable construction is used an  addition1.5 m height may be permitted at the peak of the gable. Parapet Wall: Parapet walls shall be at least 200 mm thick.  height shall not exceed 4 times the thickness. The  parapet wall shall not be thinner than the wall below.  32 SUPER-STRUCTURE

33. SUITABLE FOR SMALLER SCALE CONSTRUCTION. SUITABLE FOR SOLID MASS DESIGN. ECONOMICAL. SUITABLE FOR ARCH , VAULT OPENING. EASY TO REPAIR. CAN BE USED LOCAL MATERIALS. PRODUCE THERMAL COMFORTABLE. IT IS MOST SUITABLE WHERE THE BEARING CAPACITY OF SOIL IS HIGH. DISADVANTAGES NOT APPLICABLE IN HIGH RISE BUILDING NOT POSSIBLE TO CHANGE IN UPPER FLOOR MONOTONOUS STRUCTURE & ELEVATION. NOT POSSIBLE TO MAKE AN OPENING ANY WHERE IN THE WALL. LOW CAPABILITY OF RESISTING THE EARTH QUAKE. LIMITED HEIGHT LESS ACCEPTABLE FOR CREATING VOID SPACE. SMALLER FLOOR AREA. ADVANTAGES & DISADVANTAGES OF WALL SLAB 33 SUPER-STRUCTURE

34. Waffle slab The most technical and economical type of roofs among conventional systems. A waffle slab is flat on top, while joists create a grid like surface on the bottom.   The main element in the construction waffle slabs is waffle formwork. Suitable for span of 24’ to 54’, longer span may be possible with Posttensioning. Sources:(book name- building construction illustrated, 4 th edition Page:107 SUPER-STRUCTURE Square metal or fiberglass dome Width:19’’ to 30’’ Depth: 8’’ to 20 Rib width : 5’’ to 6’’ Slab depth:3’’ to 4’’ Rule of Thumb: depth=span/24

35. Waffle slab design Slab depth is typically 75 mm (3 in) to 130 mm (5 in) thick. As a rule of thumb, the depth should be ​ 1 ⁄ 24  of the span. The width of the ribs is typically 130 mm (5 in) to 150 mm (6 in), and ribs usually have steel rod reinforcements. The distance between ribs is typically 915 mm (3  ft ). The height of the ribs and beams should be ​ 1 ⁄ 25  of the span between columns. The width of the solid area around the column should be ​ 1 ⁄ 8   of the span between columns. Its height should be the same as the ribs. Diagram shows slab and rib width with rules of thumb formula Diagram showing waffle slab rib and Beam Heights rule of thumb formulas Diagram shows the width of the column head with rule of thumb formula Sources:(book name- building construction illustrated, 4 th edition SUPER-STRUCTURE

36. POST-LINTEL SLAB: SLAB BEAM COLUMN GROUND LOAD WIDTH DEPTH Should not be equal or grater than width of supporting columns Rule of Thumb: depth=span/16 SIZE SUPPORTED AREA 12’’ 2000sf 16’’ 3000sf 20’’ 4000sf Column spacing=Beam or Slab span Post -Lintel structures/Frame structure: Frame structures are the structures having the combination of beam, column and slab to resist the lateral and gravity loads. Source:Bangladesh National Building Code-2012(chapter:7)7.4.6 page no:146-148 36 SUPER-STRUCTURE

37. TYPES OF POST-LINTEL STRUCTURE : 1.Moment frames Moment frames resist gravity and lateral load in bending and compression. They are derived from post-and beam portals with moment resisting beam to column connections. Deformation under gravity and lateral lodes are visualized in diagram: 1 Portal with pin joints collapses under lateral load 2 Portal with moment joints at base under lateral load 3 Portal with moment beam/column joint under gravity load 4 Portal with moment /column joint under lateral load 5 Portal with all moment joint under gravity load 6 Portal with all moment joint under lateral load 7 High-rise moment frames under gravity load 8 Moment frames building under lateral load Source: G G Schierle Architectural structures Excerpts, Chapter-(17-6) 2.Braced frames Braced frames resist gravity bad in bending and axial compression, and lateral load in axial compression and tension by triangulation, much like trusses. The triangulation results in greater stiffness, an advantage to resist wind bad, but increases seismic forces, a disadvantage to resist earthquakes. SUPER-STRUCTURE

38. Braced frames as follows: 1 Single portal under gravity and lateral loads 2 A-braced portal under gravity and lateral load 3 V-braced portal under gravity and lateral load 4 X-braced portal under gravity and lateral load 5 Braced frame building without and lateral load Source: G G Schierle Architectural structures Excerpts, Chapter-(3-14) 3.Steel framing Steel framing with wide-flange profiles requires careful orientation of columns in order to achieve proper strength and stiffness to resist lateral load in both orthogonal directions. Measured by the moment of inertia, typical wide-flange columns have a stiffness ratio of about a 3:1 about the x and y-axis, respectively, yet some deep sections have stiffness ratios up to 50:1, about strong to weak axes .   1 Front view of moment resisting frame with setback floors on tap 2 Column layout in plan for moment resistance in direction 3 Column oriented for lateral support in width direction 4 Column oriented for lateral support in length direction Source: G G Schierle Architectural structures Excerpts, Chapter-(17-8) SUPER-STRUCTURE

39. 4.Framed Tube Framed tubes are a variation of moment frames, wrapping the building with a "wall" of closely spaced columns and short spandrel beams. To place the lateral resistance system on the facade rather then at the interior gives it a broader base for greater stability as well as improved rotational resistance. 1 Framed tube without interior core. 2 Framed tube with interior core. 3 Global stress diagram of framed tube. 4 Framed tube with belt and top truss for additional stiffness. Source: G G Schierle Architectural structures Excerpts, Chapter-(17-13) 5.Bundled Tube Bundled tube structures are composed of tubes framed by closely spaced columns joined to beams to form moment frames. The bundled tubes resulting from the rows of columns add lateral resistance to the structure, transferring shear between exterior columns subject to tension and compression under lateral load. 1 Square tube modules. 2 Triangular tube modules 3 Hexagonal tubes would be less effective to reduce shear lag. 4 Farmed tube shear lag. 5 Bundled tube with reduced shear lag. A Shear lag between connecting shear walls. B Peak resistance at shear wall. Source: G G Schierle Architectural structures Excerpts, Chapter-(17-16) SUPER-STRUCTURE

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