Spandrel Beams Research Articles

Torsional retrofit of spandrel beams with composite laminates

Torsional retrofit of spandrel beams with composite laminates

Evaluation of the seismic response of masonry buildings based on energy functions

AbstractThis work is based on energies evaluated from the responses of 12 stone and brick masonry systems subjected to 58 shaking table tests. The evolution of input energy during a damaging base excitation is correlated to the change of the damage patterns of the considered buildings. The comparison among energies dissipated and absorbed by the buildings during the various shocks gives some hints on strengthening strategies. It is found that damage to spandrel beams produces a more significant energy absorption than other types of damage. Copyright © 2001 John Wiley & Sons, Ltd.

Correlation of damage and analysis of R/C building: Experience from the 1995 Kobe earthquake

During the 1995 Hyogoken-Nanbu Earthquake, a reinforced concrete building, called Jeunesse Rokko, suffered intermediate damage by forming a beam-yielding (weak-beam strong-column) mechanism, which has been regarded as the most desirable earthquake resisting mechanism throughout the world. High cost to repair damage at many beam ends and poor appearance expected after the repair work made the owner decide to tear down the building. Nonlinear earthquake response analyses were conducted to simulate the behavior of the building during the earthquake. The influence of non-structural members was considered in the analysis. The calculated results were compared with the observed damage, especially the location of yield hinges and compression failure of spandrel beams, and the degree of cracking in columns and in column-girder connections.

Cracking and Punching Shear Failure Analysis of RC Flat Plates

This paper presents a nonlinear layered finite element method capable of analyzing cracking and punching shear failure of reinforced concrete flat plates with spandrel beams or torsion strips. Incorporating a layered approach with transverse shear capabilities, the procedure takes into account the full interaction between the spandrel beam and the adjoining slab (in bending, shear, and torsion). The formulation of the nonlinear cracking and failure analysis is discussed in some detail. A comparative study based on a series of 11 half-scale reinforced concrete flat plate models and four single slab-column specimens confirms the method's ability to satisfactorily predict the punching shear strengths, the deflections, and the crack patterns, as well as the collapse loads, of the models. Also included in the comparison is a semiempirical procedure, along with those recommended by the American Concrete Institute, the British Standards Institution, and the Standards Association of Australia. Results show that t...

Layered finite element method in cracking and failure analysis of RC beams and beam-column-slab connections

A nonlinear semi-three-dimensional layered finite element procedure is developed for cracking and failure analysis of reinforced concrete beams and the spandrel beam-column-slab connections of flat plates. The layered element approach takes the elasto-plastic failure behaviour and geometric nonlinearity into consideration. A strain-hardening plasticity concrete model and a smeared steel model are incorporated into the layered element formulation. Further, shear failure, transverse reinforcement, spandrel beams and columns are successfully modelled. The proposed method incorporating the nonlinear constitutive models for concrete and steel is implemented in a finite element program. Test specimens including a series of reinforced concrete beams and beam-column-slab connections of flat plates are analysed. Results confirm the effectiveness and accuracy of the layered procedure in predicting both flexural and shear cracking up to failure.

Effect of spandrel beams on strength and behaviour of column-slab connections

Spandrel beams are commonly used to strengthen the connections between slabs and edge columns in flat slab structures. The present study uses experimental and analytical means to improve understanding of the behaviour of these connections, especially when spandrel beams are used. The parameters considered are the spandrel beam size and reinforcement ratio, the width of the inside column slab interface, and the type of straining actions to be transferred through the connection. The efficiency of using a slab extension (beyond column outer face) instead of a spandrel beam is also studied. Based on the failure mechanism observed during the tests, a new analytical method to predict the strength of edge column-slab connections is suggested. A second analytical method is also developed while being based on a simplified failure surface. The accuracy and reliability of both methods are thoroughly assessed in this study.

Role of Spandrel Beams on Response of Slab-Beam-Column Connections

Full-scale exterior beam-column-slab subassemblages were tested under reversed cyclic loading to investigate the role of the spandrel beam in the overall response. Results from specimens having different spandrel beam sizes and different amounts of torsional reinforcement in the spandrel beams provided a better understanding of their behavior. Detailed strain measurements together with the crack patterns indicate that the effective width of the slab contributing to the negative bending of the main beam is affected by the torsional yielding of the spandrel beam. However, after this yielding, a different force mechanism, involving concrete compressive struts and tension ties in the slab and spandrel beam bars, provides means of transferring additional forces from the slab bars to the joint region. It is important to consider the effect of these forces, since they increase the negative moment capacity of the beams, and, hence, they may affect the hierarchy of yielding between the columns and the beams. Design proposals, accounting for the flow of forces through the spandrel beam, are presented and illustrated by a number of examples.

Effect of material properties on inelastic dynamic response of spandrel beams

Based on equilibrium and compatibility conditions as well as a tri-linear relationship for moment-curvature and torque-twist curves, a theory was presented to predict the static behaviour of reinforced concrete spandrel beams. The theory was compared to tests of 20 spandrel beams and was found to be applicable throughout the loading history. It is shown in this paper that the inelastic dynamic response of spandrel beams can be predicted using Takeda's rules for hysteresis loops and the linear acceleration step-by-step method, and an algorithm is described for the solution of such beams. Moreover, the effect of material properties on the inelastic dynamic response of such beams is systematically studied. It is found that the ductility factors of such beams are increased with increasing concrete compressive strengths; and the ductility demands are decreased with increasing concrete compressive strengths.

Seismic Repair and Strengthening of a Severely Damaged Concrete Frame

A repair technique designed to strengthen and repair reinforced concrete frames with heavily damaged columns was tested experimentally. A two-thirds scale model of two bays and two stories of an exterior moment-resisting frame with heavily damaged columns was repaired and strengthened by completely encasing the damaged columns. The damage was characterized by heavy shear cracking and spalling of the concrete in the window space between the spandrel beams. In addition to repairing the damage to the columns, the new columns were designed to increase the lateral capacity of the frame and to shift the mode of failure from shear in the columns to flexural hinging in the beams. Test results of the frame was successfully shifted from column shear failure to flexural hinging of the beams. The results also showed that the encased columns behaved monolithically, and that the lateral strength of the frame was substantially increased

Methods of punching shear strength analysis of reinforced concrete flat plates-A comparative study

The punching shear strength of concrete flat plates is one of the topics of intensive research in recent years by various concrete structures researchers. This paper reviews four current methods of analysing the punching shear strength at the corner-and edge-column positions of reinforced concrete flat plates. They include those recommended in the Australian Standard AS3600-1988, the American Concrete Institute ACI318-89 and the British Standard on Concrete Practices (BS8110) as well as the approach developed at the University of Wollongong, Australia. Based on half-scale model test results, a comparative study of these four analysis methods is made with regard to their limitation, accuracy and reliability. It is found that the Wollongong approach in general gives the best performance in predicting the punching shear strength of flat plates with torsion strips and those with spandrel beams. The Australian Standard procedure performs just as satisfactorily for flat plates with torsion strips but tends to be unsafe for those with spandrel beams. Both the ACI and the British methods are applicable only to flat plates with torsion strips; they also tend to give unsafe predictions for the punching shear strength.

Failure Due to Deficient Welding

On the afternoon of June 1, 1983, the entire facade of the new wing of a broadcasting headquarters building collapsed during construction. The wall fell suddenly and debris covered the roof setback at the sixth floor, causing damage to the framing at this level.A careful review of the collapsed area indicated that the precast spandrel beam hung from the structural steel overhangs. It was established by analytical computations and by full-scale laboratory testing that the welds are constructed were not adequate to safely support the required loads on the plates. The crucial contribution of weld returns to increased load capacities of the connection was demonstrated by laboratory testing. The tests were conducted both on sections actually retrieved from the collapse area and on equivalent, full-scale assemblies specifically constructed and welded for testing.

Punching Shear Strength Analysis of Reinforced Concrete Flat Plates With Spandrel Beams

Punching Shear Strength Analysis of Reinforced Concrete Flat Plates With Spandrel Beams

Observations on Two Seismic Strengthening Schemes for Concrete Frames

A large-scale model of a nonductile concrete frame with columns susceptible to shear failure was retrofitted with two strengthening schemes. In the first scheme, full-height concrete piers were added to the original columns. Tests showed that the strengthened column section behaved monolithically and the failure mode was shifted to hinging of the spandrel beams. Large increases in frame strength and stiffness were also realized. In the second scheme, a steel X-bracing system was attached to the frame's exterior face. Lateral capacity was governed by yielding and buckling of the braces. The system exhibited substantially increased frame stiffness and strength. Both systems were quite constructable and relied extensively on epoxy-grouted dowels. The pier system required a lower level of construction skill but was somewhat more labor intensive. The bracing system required a higher level of construction skill due to local variations in fit-up requirements and the need for field welding.

Behavior of RC Frame Strengthened Using Structural Steel Bracing

A retrofit strengthening technique for improving the seismic behavior of a nonductile reinforced concrete (RC) frame was investigated experimentally. The original frame contained deep, stiff spandrel beams and short, flexible columns that were susceptible to shear failure under lateral loads. The strengthening technique used a steel X‐bracing system attached to the exterior of the frame using epoxy‐grouted dowels. A two‐thirds‐scale frame model consisting of two bays and three levels was subjected to statically applied cyclic lateral load. Test results indicated substantial increases in both lateral stiffness and strength. The lateral capacity of the strengthened frame was governed by brace buckling and eventual connection failures and column shear failures. Measured brace buckling loads agreed well with predicted capacities assuming fixed (K=0.5) connections, and dowel performance was excellent. Bracing‐system elements attached to the side faces of the concrete columns also substantially increased column...

Redistribution of Moments in Spandrel Beams

In 1977, the ACI Building Code introduced a torsional limit design method for the design of spandrel beams subjected to torsion. This very economical method utilized the redistribution of moments between the spandrel beam and the adjoining floor beams. This paper provides a theoretical method to predict the two disticnt redistributions of moments and to clearly describe the 3-stage behavior of the spandrel beam.

Truss Model for 3‐D Behavior of R.C. Exterior Connections

The inelastic behavior of tee-beam sections at exterior reinforced concrete beam-column connections subjected to earthquake loading is investigated using a three-dimensional truss analog. This model accounts for the spatial characteristics of the response of connections, including effects of flexible transverse beams. In the analysis, longitudinal and transverse beams are modeled by line elements, and the slab is modeled by a truss connecting the longitudinal and transverse beams. The analytical model indicates that the behavior of the longitudinal beam is strongly influenced by flexural and torsional deformations in the spandrel beams. Computed results are compared to experimental results.

Seismic response of reinforced concrete frame subassemblages — a Canadian code perspective

The 1984 CSA standard for the design of concrete structures for buildings provided new seismic design and detailing requirements for concrete structures. Full-scale, reversed cyclic loading tests of reinforced concrete beam–slab–column subassemblages were carried out to investigate the seismic performance of frame structures designed with the latest Canadian code. The test results indicate the importance of including the influence of slab reinforcement in computing the beam capacity as well as the need to carefully design the joint regions for shear. The test results indicate the excellent performance of frame components designed with K = 0.7 (R = 4.0) and the poor performance of those designed and detailed with K = 2.0 (R = 1.5). The performance of subassemblages designed with K = 1.3 (R = 2.0) depends on the column to beam strength ratio and on the shear strength of the joints. Models to predict the flexural response as well as the shear response of key elements are described and the role of the spandrel beam in limiting the effective slab width is explained. Key words: seismic design, reinforced concrete, detailing, structures, codes.

Multiple stud shear connections in deep ribbed metal deck

This paper summarizes the results of push-out tests conducted on 17 different types of shear connections simulating three distinct components of a composite floor system: (1) an interior beam (perpendicular metal deck), (2) a spandrel beam (perpendicular metal deck), and (3) a girder (parallel metal deck). Each push-out specimen had a layer of 152 × 152 WM9.1 × WM9.1 welded wire mesh at mid-depth of each concrete slab.Two composite beams, each with ribbed shear connections typical of those in two of the types of push-out specimens representing ribbed shear connections in interior composite beams with ribbed metal deck, were tested with third-point loads over a simply supported span. Using the average ultimate shear strengths of the push-out specimens having the same configurations as the ribbed shear connections in the composite beam tests to calculate the ultimate flexural capacities of the composite beams resulted in a very close estimate of the measured ultimate flexural capacities of the composite beams. The average measured static yield strengths of the flanges and webs of the wide-flange sections used in the composite beam tests were included in the calculations of the ultimate flexural capacities of the composite beams. Key words: composite, push-out, ultimate shear, shear stud, ribbed metal deck, deep rib.

Behavior of Precast Reinforced Concrete Ledger Beams

he design of ledger beams, commonly used as spandrels in precast concrete structures, may not always be adequate under currently accepted criteria based on the ACI Building Code' and the PCI Design Handbook' due to insufficient accounting for minor axis bending effects, and potentially, secondary effects. This paper presents the results of a study investigating load-deformation behavior of slender ledger beams. The conclusions and design recommendations drawn may assist engineers in preventing unserviceable behavior of such members. To determine the load-deformation behavior of ledger beams, a program of experimental analysis was conducted. Six model beams were tested by progressive elastic range Ioading at seven different spans in three configurations. The configurations considered were braced major axis bending under pseudo-uniform loading, uniform torsion only, and unbraeed bending and torsion under uniform eccentric loading intended to simulate the loads on spandrel ledger beams met in practice. Measurements were made of the vertical and horizontal midspan deflections and the midspan rotation under the appropriate loading conditions. The differences between the unhraced bending behavior obtained experimentally, and those estimated by superposition of the other two loading conditions were examined for any identifiable secondary behavior, or other response of potential design interest.

Structural System--Getty Plaza Tower

In areas of strong seismic activity, the lateral load resisting structural systems for buildings need to be designed with appropriate stiffness and ductility, which are often counter objectives. Adequate stiffness is needed to resist building displacement during wind and moderate earthquake loadings, primarily in order to control damage to non-structural elements—and for taller buildings to mitigate perception of building sway during frequent wind storms. Secondly, adequate ductility is needed in the structural elements and connections as well as in the overall structural system to provide sufficient reserve of strength at large displacement to absorb severe earthquakes without building collapse. The need to provide overall building stiffness and strength at least cost has lead to development of various structural framing systems. In particular, the braced-frame and tubular framing systems have gained a wide acceptance with structural steel application. A framed-tube structure typically has closely spaced perimeter columns that are interconnected at floor levels with deep spandrel beams, thereby creating a relatively rigid peripheral grid. The shear lag along the flange frames is greatly reduced, thus improving the effective cantilever stiffness of the overall structure.