Frames and WallsLateral Stability

• A beam simply supported by two columns is not capable of resisting lateral forces unless it is braced.

• If the joints connecting the columns and beam are capable of resisting both forces and moments, then the assembly becomes a rigid frame.

• If we fill in the plane defined by two columns and a beam, it becomes a loadbearing wall that acts as a long, thin column in transmitting forces to the ground.

• Any opening in a loadbearing wall weakens its structural integrity. A lintel or arch must support the load above a door or window opening and allow the flow around the opening to sections of the wall

Lateral Stability

• The structural elements of a building must be sized, configured, and joined to form a stable structure under any possible load conditions.

• A structural system must be designed to not only carry vertical gravity loads, but also withstand lateral wind and seismic forces from any direction.

Lateral Forces

• They are considered to act parallel to the ground plane

• They may occur at many angles other than the horizontal

Types of Lateral Forces

External Lateral Forces:1.Wind Force2.Seismic Force3.Fluid pressure from water and other liquid4.Soil against a basement or retaining wall5.Sand, grain, coal or wood chips in a storage

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• Wind Load is influenced greatly by local terrain

• Upon contact with a building, it can produce pressure and suction forces on any surface of a building and the pressure will tend to balloon the building outward.

• Seismic Load – forces generated by inertia of building mass as ground moves below the structure

• The effect is internal

• Flood waters can produce devastating effect and can destroy foundations of bridges and buildings

• Internal Lateral Force – restrained movement associated with temperature change

• If prevented from expanding or contracting, a material will undergo internal forces and stresses.

Horizontal Diaphragm

• A rigid floor structure, acting as a flat, deep beam, transfers lateral loads to vertical shear walls, braced frames or rigid frames

• Rigid Frame – a steel or reinforced concrete frame with rigid joints capable of resisting changes in angular relationships.

• Shear Wall – a wood, concrete, or masonry wall capable of resisting changes in shape and transferring lateral loads to the ground foundation.

• Braced Frame – a timber or steel braced with diagonal members.

Structural Patterns

References:

• http://arch.umd.edu/Tech/Tech_III/Lectures/Lateral_Forces_&_Framing/Introduction_to_Lateral_Forces.pdf

• Building Construction Illustrated Francis DK Ching Fourth Edition