Building Structures

Enclosure Systems

(dealing with building skin) -Roof -Exterior wall -Openings: doors + windows

Mechanical Systems

(lighting, sewage, etc) -Water supply -Sewage disposal -Heat, vent, air conditioning -Electrical and communication -Vertical transportation -Fire fighting -Waste disposal/recycling

Structural systems

-superstructure (whatever's above ground) -substructure (underneath, hidden inside)

Determination of Structural Systems

1. Design a form 2. Choose the proper materials and type of structure 3. Verify that the elements and configurations work according to structural requirements

Criteria for location

1. Sufficient cover to protect steel from the environment 2. Proper spacing between the bars to ensure concrete flows around the bars

Design considerations

1. The spans involved (span from one column to another) 2. Internal space planning (depends on nature of the function) 3. External treatment (indicates expression of the form)

Column, Girder, Beam

1. _____________ 2. _____________ 3. _____________

Advantages of Precast Concrete Frames

1.Able to control the quality of materials and workmanship better than onsite (able to build in the rain, sleet, or snow) 2.Able to vibrate the concrete mechanically to achieve maximum density and highest surface quality. 3.Able to reuse formwork more than onsite, thus reducing formwork cost per unit. 4.Able to steam cure, thus accelerating curing with the steam's heat and adding moisture for full hydration.

Space Frames

3 dimensional truss. Flat plate with many holes in it Is a truss that works in 2 directions Upper chord supports compression, lower chord holds tension Most common: pyramid and tetrahedra Cover large spans (10-150 m), generally used for big buildings Made of steel bars and connectors. Joints are not rigid.

Occupancy Classifications

A. Assembly (auditoriums, theaters, stadiums) B. Business (Offices, laboratories, higher edu) E. Educational (child care facilities & schools) F. Factories H. Hazardous Uses I. Institutional (facilities for supervised occupants, hospitals, nursing homes, reformatories) M. Mercantile (stores) R. Residential (homes, apts, hotels) S. Storage (warehousing)

Structure Accepted

Aesthetical and structural programs coexist in harmony. Adaptation of one of the basic forms of structure.

5 meter span

All structural types are possible

5-10 meter range (short span structures)

All structural types are possible Optimal: load bearing wall arrangements in masonry or timber, with sample horizontal elements such as timber beams or reinforced concrete slabs

10-20 meter range

All structural types are possible except masonry and load bearing walls. Optimal: skeleton frame in either reinforced concrete or steel, and laminated timber

Roof Structures

Arches, Vaulted halls, Domes Portal frames Trusses Space frames Folded roofs Shells Membranes and Tents

Reinforcing bars

Are available in various sizes and grades. The grade designates the yield strength of the material used in the manufacture of the bars. The three most common grades are 40, 50, and 60

Trusses

Basis is triangulation. Divided into triangles. One edge of triangle is in compression and the other two edges are in tension. No bending. Used for bridges and supporting sloping roofs. Timber (span 5-11 m, h: 12-25 m) Steel (span 25-65 m, h: 12-75m) Aluminum Joints are not rigid Concept depends on distributing loads on chords

Basic Structural Elements

Beam Column Truss Arch Vault Dome

One way slabs

Beam supported floor used for small residential buildings An elevated reinforced concrete slab where most of the load on the slab is carried to the supporting beams in one direction; a four sided, supported rectangular slab whose length is greater than o r equal to twice its width.

One way joist floor

Beam supported floor used for: i. Small building. Public building ii. Two way joist floor (waffle slab) 1. Medium span 16 meters

Elevated Concrete Floors

Beam supported floors: -One way slab -Two way slab -One way joist floor -Two way joist floor (waffle slabs) Beamless floors: -Two way joist floor -Flat plate -Flat slab

Flat Plate

Beamless floor used for: i. Slab and columns ii. Lightweight structure iii. Use to reduce the height of building iv. Reduce amount of concrete used. v. Hotels, hospitals, high rise towers vi. Provides freedom for open plans

Flat Slab

Beamless floor used for: i. Heavy structure ii. Can bear heavy loads. iii. Used in multistory parking garages

Masted Structures

Buildings with tall masts which provide the high level anchorages for systems of tensile cables or rods, which in turn support the roof. Can be single mast, two mast, or four mast Vertical posts are visible from the outside

Civil Structures

Buildings, bridges, towers, etc Used by civilians or general public

Precast

Concrete cast at a factory Used in typical buildings with lots of repetition Cheaper for high rise buildings Higher quality Accurate dimensions Disadvantages: Limits creativity of the design Difficult to transport High cost for small sized projects

Forces acting on structures

Dead loads (permanent) Live loads (transient) Wind Earthquakes Storm Fluid pressures Vertical: gravity Lateral: wind, earthquake Tension Compression Bending Torsion

Pneumatic Structure

Depends on air pressure Exhibitions, show rooms

Mechanical Splicing

Depends on screwing 2 steel bars together Used in large style steel bars Used in columns Time consuming and expensive usually consists of some type of metal sleeve that is held securely in place by a wedge driven over the sleeve ends.

Folded Roofs

Flat roof which increases its strength by folding Made out of reinforced concrete Many types: cylindrical, circular, square, folded plate, portal frame, etc. Built with a minimum thickness with spans up to 20 m

Selection Criteria For Building Materials

Functional performance: In stable equilibrium, Strength, Serviceability, Safety of operation. Aesthetic qualities: Visual appearance, personal choice. Not constrained by legal constraints: Codes & ordinances . Economical : Funds available, life-cycle costs, etc. Environmentally Friendly: least damaging and disruptive, very little environment damaging effluents and emissions, etc.

Structures classifications

Geometry (planar, curvilinear) Stiffness (rigid vs flexible) Span type (one way vs 2 way) Material (wood, masonry, concrete, steel)

Steel

High strength material Used for tallest buildings and longest spans Skeleton frames, portal frames, horizontal or curved trusses, space frames, tensile structures Aesthetic: openness, celebration of technology, cold, temporal, lightness

30-60 meter range

Highly efficient fully form active structures, tents and cable networks, shells, arches, vaults

Planking

Horizontal panels which are used in forming the slab area to pour the concrete onto

Load bearing walls

Horizontal spanning elements supported on vertical walls walls made of: masonry, concrete, or timber roofs and floors are of: timber, steel or reinforced concrete Cheaper restrictive in terms of internal planning: height (6 floors), spans (6 meters), opening, design

Proportions

Horizontal: -post and beam (roof with compression: wall bearing, skeleton) -roof with tension -roof Vertical

Welded Wire Reinforcing

Its a form of concrete reinforcing consists of wire or round rods, either smooth or deformed, welded into grids. It is commonly known as welded wire mesh or welded wire fabric because the spacing between wires is relatively small. This type of reinforcement is used primarily in slabs because of ease of placement. Grids may come as sheets or rolls

Portal Frames

Joining a beam to its two supporting columns with rigid joints Rigid only on one plane Structural steel (9-60 m span) Laminated timber (12-35 m span) Reinforced concrete (12-24 m span) Can be constructed with flat or slanted roof Suitable for medium sized spans

Roof supported by columns subject to tension

Masted structures

Structural Systems

Materials: steel, wood, timber, masonry Proportion: horizontal, vertical Subsystems: Superstructure (floor, wall roof) Substructure (foundation) Span Type: wide, medium, short

Lap Splices

Most commonly used. Cost efficient and don't need special hardware Join 2 bars with small steel wires Used in normal sized steel bars

Building Codes

National/International Speaks about the minimum issue (ex. minimum width of corridor in a mall) Building can't be built if it doesn't follow the code "a group of statements for specific requirements to Establish minimum construction standards for the protection of life, health, and welfare of the public"

Welded splices

Only used in special connections/odd shaped connections Avoid in small steel bars Normally avoided because heat may affect properties of the steel

Roofs supported by columns subject to compression

Post and beam structures: -load bearing walls -skeleton frame

Normal reinforcing

Preparing the steel bars and pouring the form of the concrete

Structural Sub System

Roof Walls Floors Framing Foundations (substructure)

Construction Concerns

Safety, built on time, within budget, quality of construction, sequencing of construction operations, inclement weather, quality assurance of materials, etc.

Concrete Components

Sand (fine aggregate) Gravel (coarse aggregate) Cement (binder) Water Air

Military Structures

Ships, aircrafts frames, tanks, etc Used by military

20-30 meter range

Skeleton frame in steel (space framework) and laminated timber or portal framework. Reinforced concrete is less common.

Pretentioning

Steel is stretched and then the concrete is poured Accomplished by stressing wires or strands, called tendons, to predetermined amount by stretching them between two anchorages prior to placing concrete the concrete is then placed and tendons become bounded to concrete throughout their length. After concrete has hardened, the tendons are released by cutting them at the anchorages.

Characteristics of a Structure

Strength Stability Economic Value Serviceability (respecting the function) Environmental Conditions

Building systems

Structural systems: -superstructure (whatever's above ground) -substructure (underneath, hidden inside) Enclosure Systems (dealing with building skin) -Roof -Exterior wall -Openings: doors + windows Mechanical Systems (lighting, sewage, etc) -Water supply -Sewage disposal -Heat, vent, air conditioning -Electrical and communication -Vertical transportation -Fire fighting -Waste disposal/recycling

Subsystems

Superstructure: -floor -wall -roof (low/flat, pitched) Substructure: -foundation

Tensile Structures

Tensile equivalent of domes and vaults. Internal forces are axial but in tension, and are highly efficient in resisting loads Used when high structural efficiency required: long spans w/ lightweight structure Two types: membranes and masted structures

Structure Ignored

The architect disregards structural considerations when determining the form of a building

Structure Dominant

The design of the structure is the highest priority and allowed determining completely both the overall form of the building and the nature of its architectural vocabulary

Arches, Vaulted Halls, Domes

The dominant feature is an upward curvatures towards the dominant, downward acting gravity load---depends on curvature of the structure. Transfer loads from one to another gradually Internal forces are predominantly axial and in compression Allows large horizontal spans with materials of little tensile capacity (eg. masonry, reinforced concrete) Very lightweight structures Masonry (10 m span) Reinforced concrete (60 m) Timber (100 m)

Structure Symbolized

The structure is emphasized visually and constitutes an essential element of the architectural vocabulary

Formwork

The term given to either temporary or permanent molds into which concrete or similar materials are poured

Membranes

Undulating mesh of steel cables, the peaks of which are either drawn up from above, using the external masts, or propped up by the internal masts from below Can adopt the form of shells (50-180 m span)

Timber

Used as horizontal elements (floors and roofs) of post and beam structures, as skeleton frames, as sloping roofs with rafters, domes, vaults, arches, and shell forms Aesthetic: Natural, organic, warm

Reinforced concrete

Used for load bearing walls, skeleton frames, arches, vaults, folded roofs, and shells Aesthetic: Freedom, stability, permanency, solidity

Masonry

Used for small and medium spans in the form of load bearing walls (vertical elements) and arches, vaults and domes (horizontal elements) Aesthetic: Warm, heaviness, permanency, craftsmanship

Scaffolds

Vertical steel elements which support as a temporary structure or platform for supporting workers and materials at a height

Metalwork

When using metal sheets in formwork process. Can be used instead of timber Used in large sized projects because the final result is neater Reusable

Timberwork

When using timber in the formwork process Not a clean finish, but cheaper Reusable in rare cases

Vertical Structural Systems

X or Y < Z Wind, lateral, earthquake, Main concern: walls

Horizontal Structural Systems

X or Y > Z Bending, compression, tension Main concern: roof

System

an assembly of interrelated or interdependent parts forming a more complex and unified whole to serve a common purpose

Roof structures

arches, vaulted halls, domes portal frames trusses space frames folded roofs shells membranes and tents

Shells

belong to the family of arches, vaulted halls and domes huge span, lightweight roof Generally made out of reinforced concrete (40 m to 73 m) If combined with space frames and lattices then spans can reach up to 200 meters

Virendeels structures

depends on having a wide span and deep slab with lightweight roof, used for auditoriums and theaters Require less depth, carry more load, have less deflection, and resist lateral and gravity loads. One way, two way, and three way spans. Two way better for orthogonal plans, three way better for triangular, hexagonal or free form

Skeleton Frame

horizontal spanning elements supported on vertical columns, beams, and columns which support floor slabs and roof cladding Steel (30 m span) Reinforced concrete (20 m) Timber (30 m) Beams and columns provide great freedom in design because walls aren't load bearing

Post and beam structure

most architectural structures are ______________ carry the weight of their structural components by bearing on one another weight of roof and beams carried by the posts down to the foundations and then into the ground horizontal beams are subject to bending loads and are able to resist tension and compression Further subdivided into load bearing walls and skeleton frame

Structure

refers to a system of connected parts that can support loads while performing its primary functions Primary purpose of building ___________ is to transmit support and transmit the building loads and forces to the ground

Building codes mission

regulate building activities Define user groups, construction types, fire resistance ratings, materials, natural light, ventilation,, structural design, construction methodology, fire protection systems, accessibility to disabled persons,, etc. Provision for interior finishes, fire protection systems, interior environment, energy efficiency, emergency exits, exterior walls and roofs.

Two way slabs

slabs are supported continuously on all four sides Beam supported floor used for: i. Squares ii. Institutional buildings—office, commercial facilities iii. Medium spans

30 cm columns

support up to 185 square meters

40 cm columns

support up to 280 square meters

50 cm columns

support up to 372 square meters

Posttensioning

the tendons are stressed and each end is anchored to the concrete section after the concrete has been cast Pour the concrete and leave holes in the concrete and then place steel bars in the concrete and then stretch the steel bars. Provides more strength to the street. Heavy loads, bridges involves first forming and casting the member with ducts through its length. After the concrete is cured, reinforcement is placed in the ducts and anchored at one end. It is stretched against the concrete by means of jacks. The tendons are gripped and tension is maintained by various patented gripping devices that fit into the end of the member. used to add stability to the overall frame by providing a fixed connection between the beams and columns.

Prestressing

the tensile reinforcement has been placed under tension before the member is erected.