Civil Engineering Reference
In-Depth Information
Appendix B
Damage to Structures
B.1 Structural Defi ciencies
Failure modes observed in existing structures during past earthquakes worldwide were caused by a
number of member, connection and system defi ciencies. Some of these defects are summarized below
for buildings and bridges, respectively.
B.1.1 Buildings
Generally, defi ciencies in building structures are classifi ed as structural and non- structural. The former
refers to: (i) sections, (ii) members, e.g. beam-columns and braces, (iii) connections, (iv) diaphragms,
(v) foundations and (vi) structural systems. Non- structural defi ciencies comprise: (i) suspended ceilings,
(ii) exterior ornamentation, (iii) mechanical and electrical utilities, (iv) poor construction quality and
(v) deterioration. This section chiefl y focuses on design defects of structural components.
Common structural defi ciencies and design defects in reinforced concrete (RC) buildings include:
(i) Poor quality and inadequate detailing;
(ii) Excessive and unexpected member overstrength, especially for dissipative components;
(iii) Change of material and detailing at intermediate fl oors. In some cases, the bottom storeys may
be constructed from composite (steel/composite) changing to RC at an upper level. Deforma-
tion demand may be concentrated at the fl oor, where the change occurs;
(iv) Reduction in column dimensions due to high overstrength if uniform sections are used at higher
storeys. An abrupt change in stiffness and strength may lead to failure at the level of change,
since the fl oor load above and below is similar;
(v) Inadequate storey shear strength caused by an insuffi cient number of columns and walls;
(vi) Irregularities of mass, stiffness and strength distribution in plan and elevation (
see
Sections
A.1.1 and A.1.2). Torsional effects may be caused by non-coincidence on the fl oor plan of the
centre of gravity and the centre of stiffness as discussed in Sections 2.3.1.2 and A.1 ;
(vii) Low structural redundancy, e.g. insuffi cient number of lateral resisting systems;
(viii) Large openings in fl oor diaphragms due, for example, to the presence of stairwells and lifts as
illustrated in Section 2.3.2.2 ;
(ix)
Inadequate separation joints between adjacent buildings, especially for buildings with different
heights and different materials of construction;
(x)
Large differential displacements due to settlement of the foundation system.
