Civil Engineering Reference
In-Depth Information
Chapter 4
Case Study of a Full Scale RFERS in Service
Abstract.
A distressed Rigidly Framed Earth Retaining Structure (RFERS) open
concrete garage that retains 11 m (36 ft) of soil was instrumented. After some
repairs, movement of the building was monitored and recorded hourly. The
monitoring revealed complex temperature-dependent soil structure interactions,
which are reported in this chapter.
4.1 Introduction
A structural condition survey of a partially underground (hillside) car parking
structure revealed the presence of lateral deformations on the order of a few
centimeters that led to severe structural distress. The structure, shown in Fig. 4.1 and
labeled PG-1 hereafter, is a four-story reinforced concrete building including a full
basement, with a rectangular footprint measuring 52.42 m by 71.32 m (172 ft by 234
ft). The building's structural system, shown in Fig. 4.2, consists of reinforced
concrete waffle slabs supported by rectangular reinforced-concrete columns.
The north side of the building is a reinforced concrete retaining wall cast
against earth at full height with a thickness of 457 mm (18 in) at the base tapering
down to 305 mm (12 in) on top. On the southern side, a one-story high, 305-mm
(12-in) thick, cast-in-place concrete wall provides enclosure for the basement. The
floor slabs are cast monolithically with the wall and steel reinforcement extended
in the slab and wall. Resistance to lateral loads is provided by (1) the northern
retaining wall, (2) irregularly placed concrete walls at the eastern edge, and (3) the
lateral stiffness of the reinforced concrete frame.
The building is openon three sides and is subject to large temperature
variations.Fig. 4.3 illustrates a longitudinal section of PG-1.
An optical survey revealed that the structure underwent a maximum lateral drift
of 76 mm (3 in) in the north-south direction, and a drift of 25 mm (1 in) in the east-
west direction, at the roof level, during its 25 years of service. The amount of
deflection measured decreased from the highest to the lowest level, which is similar
to the deflection of rigid frames subjected to lateral loads. The large movements in
both building directions indicate the presence of torsion, which is associated with
the lack of symmetry in the lateral load resisting elements. This lateral-torsional
movement induced severe cracking in several columns on the fourth-story level and
the failure of one column at the same level (Fig. 4.4).
