BSD- MOD 2

Structural System

n providing support for other building systems and our activities in it, a structural system enables the shape and form of a building and its spaces, similar to the way in which our skeletal system gives shape and form to our body and support to its organs and tissues.

Structural Systems

it requires that we consider the manner in which the overall configuration and scale of structural elements, assemblies, and connections encapsulate an architectural idea, reinforce the architectural form and spatial composition of a design proposal, and enable its constructability.

18th century

masonry-bearing wall systems (or using stones) dominated building designs until the advent of iron and steel construction

Structural System

concealed or obscured by the exterior cladding and roofing of the building

Substructure

serves as the foundation of the building. Its main job is to safely transmit loads into the ground while supporting and securing the superstructure above. Foundations must be planned to adapt to the various soil, rock, and water conditions below as well as the shape and arrangement of the superstructure above.

Substructure

Its primary function is to support and anchor the superstructure above and transmit its loads safely into the earth.

Substructure

the lowest division of a building—its foundation—constructed partly or wholly below the surface of the ground.

Relation to superstructure

The type and pattern of required foundation elements impact, if not dictate, the layout of supports for the superstructure. Vertical continuity in load transmission should be maintained as much as possible for structural efficiency

Soil type

The integrity of a building structure depends ultimately on the stability and strength under loading of the soil or rock underlying the foundation. The bearing capacity of the underlying soil or rock may therefore limit the size of a building or require deep foundations.

Relation to topography

The topographic character of a building site has both ecological and structural implications and consequences, requiring that any site development be sensitive to natural drainage patterns, conditions conducive to flooding, erosion, or slides, and provisions for habitat protection.

Shallow Foundations

employed when stable soil of adequate bearing capacity occurs relatively near to the ground surface.

Spread Foundations (Shallow)

They are placed directly below the lowest part of a substructure and transfer building loads directly to the supporting soil by vertical pressure.

Deep Foundations

Consist of caissons or piles that extend down through unsuitable soil to transfer building loads to a more appropriate bearing stratum of rock or dense sands and gravels well below the superstructure.

Superstructure

the vertical extension of a building above the foundation, consists of a shell and interior structure that defines the form of a building and its spatial layout and composition

Shell

envelope of a building, consisting of the roof, exterior walls, windows, and doors, provides protection and shelter for the interior spaces of a building.

Structure

required to support the shell of a building as well as its interior floors, walls, and partitions, and to transfer the applied loads to the substructure.

Bulk-active structures

these structures redirect external forces primarily through the bulk and continuity of its material, such as beams and columns

Vector-active structures

these structures redirect external forces primarily though the composition of tension and compression members, such as a truss

Surface-active structures

these structures redirect external forces primarily along the continuity of a surface, such as a plate or shell structure

Form-active structures

these structures redirect external forces primarily through the form of its material, such as an arch or cable system

proportions of structural elements

give us visual clues to their role in a structural system as well as the nature of their material

Structural Analysis

occur only if given a specific structure and certain load conditions.

Structural Design

design activities, must operate in an environment of uncertainty, ambiguity, and approximation.

STRUCTURAL OPTIONS

how these choices might influence, support, and reinforce the formal and spatial dimensions of a building design idea

Butt joints

allow one of the elements to be continuous and usually require a third mediating element to make the connection

Overlapping joints

allow all of the connected elements to bypass each other and be continuous across the joint

molded or shaped joints

form a structural connection

Pin or hinge joints

allow rotation but resist translation in any direction.

Roller joints or supports

allow rotation but resist translation in a direction perpendicular into or away from its face.

Rigid or fixed joints

maintain the angular relationship between the joined elements, restrain rotation and translation in any direction, and provide both force and moment resistance.

Cable supports or anchorages

allow rotation but resist translation only in the direction of the cable.

Building Design

Is there an overarching form required or does the architectural composition consist of articulated parts? If so, are these parts to be hierarchically ordered

Building Design

Are the principal architectural elements planar or linear in nature?

Building Program

Are there required relationships between the desirable scale and proportion of the program spaces, the spanning capability of the structural system, and the resulting layout and spacing of supports?

Is there a compelling spatial reason for one-way or two-way spanning systems?

Systems Integration

How might the mechanical and other building systems be integrated with the structural system?

Code Requirements

What are the building code requirements for the intended use, occupancy, and scale of building?

What is the type of construction and what are the structural materials required?

Economic Feasibility

How might material availability, fabrication processes, transportation requirements, labor and equipment requirements, and erection time influence the choice of a structural system? Is there a need to allow for expansion and growth either horizontally or vertically?

Legal Constraints

There exists a regulated relationship between the size (height and area) of a building and its intended use, occupancy load, and type of construction. Understanding the projected scale of a building is important because a building’s size is related to the type of structural system required and the materials that may be employed for its structure and construction.

Zoning Ordinances

constrain the allowable bulk (height and area) and shape of a building based on its location in a municipality and position on its site, usually by specifying various aspects of its size.

International Building Code®

limit the maximum height and area per floor of a building according to construction type and occupancy group, expressing the intrinsic relationship between degree of fire resistance, size of a building, and nature of an occupancy.

Assembly

includes auditoriums, theaters, and stadiums

Business

includes offices, laboratories, and higher education facilities

Educational

includes child-care facilities and schools

Factory and Industrial

includes fabricating, assembling, or manufacturing facilities

High hazard

includes facilities handling a certain nature and quantity of hazardous materials

Institutional

includes facilities for supervised occupants such as hospitals, nursing homes, and reformatories

Mercantile

includes stores for the display and sale of merchandise

Residential

includes homes, apartment buildings, and hotels

Storage

includes warehousing facilities

Type I buildings

their major building elements constructed of noncombustible materials, such as concrete, masonry, or steel. Some combustible materials are allowed if they are ancillary to the primary structure of the building.

Type II buildings

similar to Type I buildings except for a reduction in the required fire-resistance ratings of the major building elements

Type III buildings

noncombustible exterior walls and major interior elements of any material permitted by the code.

Type IV buildings (Heavy Timber, HT)

noncombustible exterior walls and major interior elements of solid or laminated wood of specified minimum sizes and without concealed spaces

Type V buildings

structural elements, exterior walls, and interior walls of any material permitted by the code.

redundancy and continuity

apply not to a specific material or to an individual type of structural member, such as a beam, column, or truss, but rather to a building structure viewed as a holistic system of interrelated parts.

failure of a building structure

result from any fracturing, buckling, or plastic deformation that renders a structural assembly, element, or joint incapable of sustaining the load-carrying function for which it was designed

factor of safety

expressed as the ratio of the maximum stress that a structural member can withstand to the maximum stress allowed for it in the use for which it is designed.

elastic deformation

force is applied and as it returns to its original shape when the force is removed

inelastic deformation

which the element is unable to return to its original shape. To resist such extreme forces, elements should be constructed of ductile materials.

Ductility

the property of a material that enables it to undergo plastic deformation after being stressed beyond the elastic limit and before rupturing

Ductility

a desirable property of a structural material, since plastic behavior is an indicator of reserve strength and can often serve as a visual warning of impending failure

Redundancy

providing multiple load paths whereby forces can bypass a point of structural distress or a localized structural failure

Progressive collapse

described as the spread of an initial local failure from one structural member to another, eventually resulting in the collapse of an entire structure or a disproportionately large part of it

Continuity

provides a direct, uninterrupted path for loads through a building’s structure, from the roof level down to the foundation.

Continuous load paths

ensure that all forces to which the structure is subjected can be delivered from the point of their application to the foundation.

Strong connections

increase the overall strength and stiffness of a structure by enabling all of the building elements to act together as a unit

Inadequate connections

represent a weak link in a load path and are a common cause of the damage to and collapse of buildings during earthquakes

Rigid, non-structural elements

isolated properly from the main structure to prevent attracting loads that can cause damage to the non-structural members and, in the process, create unintended load paths that can damage structural elements.