Structure is a device for channeling loads that result from the use or presence of the building in relation

to the ground.

All physical objects have structures. Consequently, the design of structures is part of the general problem of

design for all physical objects. It is not possible to understand why buildings are built the

way they are without having some knowledge and understanding of the problems of their structures.

Life Safety

• This is a major concern in structures.Two prime considerations:

1.Resistance to fire 2.Low likelihood of collapse under loads.

• Combustibility of the Structure. If structural materials are combustible, they will contribute fuel to the fire as well as hasten the collapse of the structure

• Loss of Strength at High Temperature. This consists of a race against time, from the moment of inception of the fire to the failure of the structure – a long interval increasing the chance for the occupants to escape.

• Containment of Fire. Fires usually start at a single location, and preventing their spread is highly desirable.Walls , floors, and roofs should resist burn- through by the fire.

• Major portions of the building code regulations have to do with aspects of fire safety.

• Materials, systems, and details of construction are rated for fire resistance on the basis of tests.

Building fire safety involves more than structural behavior.

• Clear exit paths, proper exits, detection and alarm system, firefighting devices ( sprinklers, standpipes, hose cabinets, etc) and lack of toxic or highly combustible materials are also important.

• The structure must also sustain loads, safety in this case consisting of some margin of structural capacity for the actual task.

• This margin is expressed by the safety factor, SF.

• If the structure is required to carry 40, 0000 lbs. And is actually able to carry 80,000, the safety factor is 2.0.

General Concerns:

• Feasibility. Structures are real and must use materials

and products that are available and can be handled by existing craftspeople and production organizations. Building designers must have a grasp of the current inventory of available materials for building construction.

• Consideration must be given to the complexity of the design, cost, construction time, acceptability of code-enforcing agencies.

• Economy.Buildings cost a lot, and investors are seldom carefree with the cost of structures.A particular structure may have high performance efficiency and low cost in its own right but may produce forms and details that make other aspects of the building construction difficult and expensive.

Optimization

• Building designers often are motivated by desires for originality and individual expression.

• They are also pressured to produce a practical design in terms of function and feasibility.

• This requires making decisions that balance between conflicting considerations.

• Obvious conflicts are those between desires for safety, grandeur of spaces and generosity and practical feasibility and economy on the other.

• All of these may be important, but some rank ordering of the various attributes is generally necessary, with the cost usually ending up high on the list.

• Thus the best solution may have to be qualified in terms of the specific priorities used in the design.

• Reference: Building Construction Illustrated 4th edition Francis D. K. Ching John Wiley & Sons