Civil Engineering Reference
In-Depth Information
dampers allow serviceability deflection objectives to be met in
a materially efficient manner.
16.4.2 Reinforced, post‑tensioned and precast concrete
(light and normal weight)
Structural concrete exhibits the following material in‑service
characteristics, and structural design and calculation of move‑
ments should account for these issues:
Applied load deformation is elastic and plastic below and above
16.4 In‑service performance of structural
materials
16.4.1 Steelwork
Structural steel exhibits the following material in‑service char‑
acteristics, and structural design and calculation of movements
should account for these issues:
■
yield stress.
Response to environmental changes and applied loads is broadly
■
isotropic, although unidirectional cracking is common in incor‑
rectly designed and constructed structures.
Response to low temperatures (i.e. non‑fire) loads is linear elastic.
applied load deformation is linear elastic up to the yield stress and
■
plastic thereafter;
response to environmental changes and applied loads is isotropic;
■
■
Shrinkage, strength gain and cracking are all affected by environ‑
■
mental humidity.
Lightweight concrete properties are heavily aggregate depend‑
response to low temperatures (i.e. non‑fire) loads is linear elastic;
■
■
non‑corrosive response to environmental humidity changes is
■
ent; for equivalent concrete strengths its elastic properties, com‑
pressive and tensile strength, creep properties, durability and fire
resistance differ from those of normal concrete.
Element corrosion and degradation response is expansive.
negligible;
element corrosion response is expansive;
■
■
creep rate is low and implicitly included in codified stress-strain-
■
temperature formulae;
high creep rates in fires are dependent on rate of heating, tempera‑
Creep is dependent on mix design, environmental conditions
■
and loading, and in non‑standard or large elements a key design
consideration.
■
ture and applied member stress;
fatigue failure is possible under cyclical loading.
Structural concrete has three types of dimensional tolerance:
Manufacturing tolerances: constituent materials and mixes are
■
■
Structural steel has three types of dimensional tolerance:
naturally variable.
Environmental tolerances: dependent on actual mix poured and
manufacturing tolerances; plate thickness, flatness and section
■
■
dimensions;
fabrication tolerances; dependent on workshop quality control;
reinforcement placed.
Erection tolerances: dependent on site construction quality control.
■
■
erection tolerances; dependent on site construction quality
■
European and American codes of practice and material standards
are well developed with respect to manufacturing, environmental
and erection tolerances. In most cases the inherent improbability
of all unfavourable extreme deviations occurring together is
small, and simple means of on‑site adjustment can be incorpo‑
rated to avoid the cumulative accumulation of deviations. These
include packing pieces at non‑structural connections, whilst slabs
can either be ground or coated with liquid latex to smooth out
imperfections. See Section 16.10 for further references.
However, the designer should also be aware of anisotropic
effects in RC slabs when concrete expansion or contraction
movements are restricted, or when the aspect ratio of panels is
excessive. In such cases, cracking can be uni‑directional unless
appropriate levels of reinforcement are specified.
Tighter specification of movements and tolerances may be
required in the following cases:
control.
European and American codes of practice and material stand‑
ards are well‑developed with respect to manufacturing, fab‑
rication and erection tolerances. In most cases the inherent
improbability of all unfavourable extreme deviations occurring
together is small, and simple means of on‑site adjustment can
be incorporated to avoid the cumulative accumulation of devia‑
tions. These include packing pieces, slotted holes and threaded
rods. See Section 16.10 for further references.
Tighter specification of movements and tolerances may be
required in the following cases:
High‑rise tower lift shafts: steelwork verticality and horizontal de‑
■
flection under wind load need to be carefully controlled in line
with lift manufacturer specifications.
High‑rise tower external columns: coordination tolerances with
■
facades are crucial.
Architecturally exposed structural steel (AESS): high‑quality con‑
High‑rise tower lift shaft construction: wall verticality and hori‑
■
zontal deflection under wind load need to be carefully controlled
in line with lift manufacturer specifications.
High‑rise construction where floor pre‑setting is used to control
■
nections and details.
Fatigue‑sensitive connections: quality control of welding and
■
■
differential movement.
Architecturally exposed or unfinished concrete: high‑quality pan‑
connections.
■
See Chapter 18:
Steelwork
, for more information on steel.
els and joints.
