Tying Elements Together

DOE-STD-1020-2002

Less ductile materials, such as concrete and unit-masonry, require steel reinforcement to

provide the ductility characteristics necessary to resist seismic forces. Concrete structures

should be designed to prevent concrete compressive failure, concrete shearing failure, or loss of

reinforcing bond or anchorage. Compression failures in flexural members can be controlled by

limiting the amount of tensile reinforcement or by providing compression reinforcement and

requiring confinement by closely spaced transverse reinforcing of longitudinal reinforcing bars

(e.g., spirals, stirrup ties, or hoops and supplementary cross ties). Confinement increases the

strain capacity and compressive, shear, and bond strengths of concrete. Maximum confinement

should be provided near joints and in column members. Failures of concrete in shear or diagonal

tension can be controlled by providing sufficient shear reinforcement, such as stirrups and

inclined bars. Anchorage failures can be controlled by sufficient lapping of splices, mechanical

connections, welded connections, etc. There should be added reinforcement around openings

and at corners where stress concentrations might occur during earthquake motions. Masonry

walls must be adequately reinforced and anchored to floors and roofs.

A general recommendation for good seismic detailing is to proportion steel members

and to reinforce concrete members such that they can behave in a ductile manner and provide

sufficient strength so that low ductility failure modes do not govern the overall seismic response.

In this manner, sufficient energy absorption capacity can be achieved so that earthquake motion

does not produce excessive or unacceptable damage.

Tying Elements Together - One of the most important attributes of an

earthquake-resistant structural system is that it is tied together to act as a unit. This attribute not

only aids earthquake resistance; it also helps to resist high winds, floods, explosions, progressive

failure, and foundation settlement. Different parts of building primary structural systems should

be interconnected. Beams and girders should be adequately tied to columns, and columns should

be adequately tied to footings. Concrete and masonry walls should be anchored to all floors and

roofs for out-of-plane lateral support. Diaphragms that distribute lateral loads to vertical

resisting elements must be adequately tied to these elements. Collector or drag bars should be

provided to collect shear forces and transmit them to the shear-resisting elements, such as shear

walls or other bracing elements, that may not be uniformly spaced around the diaphragm. Shear

walls must be adequately tied to floor and roof slabs and to footings and individual footings must

be adequately tied together when the foundation media is capable of significant differential

motion.

Influence Of Nonstructural Components - For both evaluation of seismic response

and for seismic detailing, the effects of nonstructural elements of buildings or equipment must be

considered. Elements such as partitions, filler walls, stairs, large bore piping, and architectural

facings can have a substantial influence on the magnitude and distribution of earthquake-induced

forces. Even though these elements are not part of the lateral force-resisting system, they can

stiffen that system and carry some lateral force. In addition, nonstructural elements attached to

the structure must be designed in a manner that allows for seismic deformations of the structure

without excessive damage. Damage to such items as distribution systems, equipment, glass,

plaster, veneer, and partitions may constitute a hazard to personnel within or outside the facility

and a major financial loss; such damage may also impair the function of the facility to the extent

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