Spandrel Beams Research Articles

Long-term lateral deflection of precast, prestressed concrete spandrel beams

Slender precast concrete spandrels are used to increase cost effectiveness of precast concrete parking structures. They reduce the number of column lines in building floor plans and the number of elements to transport and erect. However, these spandrels can be prone to larger deflections, as the increased slenderness can reduce sectional stiffness. Design of these structures should also consider vertical and lateral deflections because of the eccentric loading transferred from the deck double-tee beams. In this paper, the authors provide realistic estimates of long-term deflections for the next generation of spandrels. They also examine the sensitivity of long-term deflection to parameters such as spandrel type, span length, creep and load eccentricity. The results of their numerical study included the finding that long-term lateral deflections are less than corresponding lateral deflections.

Seismic behavior of reinforced concrete interior beam-column joints with beams of different depths

Current Design Codes for Reinforced Concrete (RC) interior beam-column joints are based on limited experimental studies on the seismic behavior of eccentric joints. To supplement existing information, an experimental study was conducted that focused on the effect of eccentricity of the deeper beams with respect to the shallow beams. A total of eight one-third scale interior joints with beams of different depths were subjected to reverse cyclic loading. The primary variables in the test specimens were the amount of joint transverse reinforcement and the cross section of the shallow beams. The overall performance of each test assembly was found to be unsatisfactory in terms of joint shear strength, stiffness, energy dissipation and shear deformation. The results indicated that the vertical eccentricity of spandrel beams in this type of joint led to lower capacity in joint shear strength and severe damage of concrete in the joint core. Increasing the joint shear reinforcement was not effective to alter the failure mode from joint shear failure to beam yielding which is favorable for earthquake resistance design, whereas it was effective to reduce the crack width at the small loading stages. Based on the observed behavior, the shear stress of the joint core was suggested to be kept as low as possible for a safe and practical design of this type of joint.

Development of a rational design methodology for precast concrete slender spandrel beams: Part 2, analysis and design guidelines

This paper summarizes the results of an analytical research program undertaken to develop a rational design procedure for normalweight precast concrete slender spandrel beams. The analytical and rational models use test results and research findings of an extensive experimental program presented in the companion paper Development of a Rational Design Methodology for Precast Concrete Slender Spandrel Beams: Part 1, Experimental Results, which appeared in the Spring 2011 issue of PCI Journal. The overall research effort demonstrated the validity of using open web reinforcement in precast concrete slender spandrel beams and proposed a simplified procedure for design. The webs of such slender spandrels, particularly in their end regions, are often heavily congested with reinforcing cages when designed with current procedures. The experimental and analytical results demonstrate that open web reinforcement designed according to the proposed procedure is safe and effective and provides an efficient alternative to traditional closed stirrups for precast concrete slender spandrel beams.

Elastic Solutions for Eccentrically Loaded, Slender, Rectangular Spandrel Beams

AbstractSpandrel beams in precast concrete buildings are widely used to support double-tee deck beams, particularly in parking garages. Spandrel beams of deep cross-sections, resisting eccentric loads from double-tee beams, can be susceptible to excessive lateral deformations and serviceability failures before reaching their strength limits. However, closed-form solutions for estimating lateral deflections in such members are not available in the technical literature. In this paper, approximate analytical solutions for the deflection of beams with thin rectangular sections are derived from second-order elastic analysis, and they are proposed for use in estimating maximum lateral deflections in spandrel beams under eccentric and uniformly distributed loads. Continuous lateral support is provided at the elevation of the floor deck to the spandrel beams. Thus, two cases are considered: one for laterally restrained beams under typical service conditions, and a second for laterally unrestrained beams prior to ...

Effect of Spandrel Beam to Double Tee Connection Characteristic on Flexure-Controlled Precast Diaphragms

Precast spandrel beams are often used on the perimeter of precast buildings to support the precast floor units. These elements are typically not considered part of the lateral force resisting system. However, the presence of the spandrel beams in the floor system may modify the strength, stiffness, and deformation capacity of the precast floor diaphragm. The nature of this response is highly dependent on the characteristics of the details connecting the spandrel to the precast floor system. These details are often welded connections used primarily for erection stability and designed without diaphragm action in mind. With emerging design methodologies for precast diaphragms requiring better-defined performance, the impact of the spandrel beams must be accounted for. Accordingly, analytical research is presented here that examines the effect of spandrel-beam-connecting details on the global characteristics and local demands of a flexure-controlled precast floor diaphragm. Design recommendations are provided.

Development of a rational design methodology for precast concrete slender spandrel beams: Part 1, experimental results

This paper summarizes test results of an extensive experimental program undertaken to develop a rational design procedure for precast concrete slender spandrel beams. Experimental research findings presented in this paper are used to propose a rational design procedure that will be presented in a forthcoming companion paper. The research introduced significantly simplified detailing requirements for the end regions of precast concrete slender spandrel beams. Such regions are often congested with heavy reinforcing cages when designed according to current procedures. In total, 16 full-scale precast concrete spandrel beams were tested to failure to study the limit state behavior. Each specimen was loaded through full-scale double-tee deck sections to mimic typical field conditions. Three of the specimens were designed and detailed with closed stirrups, according to current practice, and served as controls for the experimental program. The remaining thirteen specimens were designed with various configurations of open web reinforcement. Several specimens were specially configured with flexural, ledge/corbel, and hanger reinforcement in excess of what would be provided in a normal design. The enhanced reinforcement helped to delay typical midspan and local failure modes and allowed for observation and study of failure modes in the end region. The experimental results, combined with the analytical results and rational modeling in the companion paper, demonstrate that properly designed open web reinforcement is a safe, effective, and efficient alternative to traditional closed stirrups for precast concrete slender spandrel beams that have an aspect ratio of 4.6 or greater.

Parametric and comparative study of spandrel beam effect on the punching shear strength of reinforced concrete flat plates

SUMMARYThe safe and efficient construction of reinforced concrete flat plate systems requires an accurate, reliable and universally applicable procedure for the punching shear strength design. A nonlinear layered finite element method (LFEM) capable of analysing the punching shear strength of such system has been developed. Based on the LFEM, a parametric study is undertaken to evaluate some of the factors influencing punching shear strength of reinforced concrete flat palate with spandrel beams. This is done by varying the depth and the width of the spandrel beam while keeping other variables constant. The numerical results obtained by the LFEM are also compared with those predicted by the recommendations of the Australian Standard (AS3600‐2009) and the Wollongong‐Griffith (W‐G) semi‐empirical method. The results confirm that the Australian Standard is inadequate in predicting the punching shear strength at the corner and edge column connections of flat plates with spandrel beams or torsion strips. Copyright © 2010 John Wiley & Sons, Ltd.

Finite element modeling of prestressed concrete spandrel beams

Nonlinear three-dimensional finite element modeling of precast, prestressed concrete spandrel beams is a challenging task and requires exploration of the effects of material parameters and modeling assumptions. To this end, the numerical results obtained using the commercial software ABAQUS/Standard were compared with existing experimental data. The sensitivity of the spandrel beam response to various parameters such as finite element type, dilation angle, fracture energy, tension stiffening, bearing stress distribution and support representation was investigated. The behavior of precast, prestressed concrete spandrels under vertical loading was found to be sensitive to the type of element, the dilation angle for the concrete, bearing stress distribution at the supports, and deck-tie stiffness. Many of the findings reported are believed to be applicable to other types of reinforced concrete structures.

Method for approximate analysis of cracking effect on lateral stiffness of reinforced concrete framed-tube structures

The paper presents analysis of framed-tube of tall reinforced concrete buildings subjected to horizontal loads. Authors take a cracking effect of frame spandrel girders of structure into account. Paper introduces simplified theoretical model of work of this kind of structures. The theoretical analysis and statistical multi-parameter numerical study of various framed-tube structures became the basis for developing a simplified assessment method of effective inertia moments of cracked spandrel beams.

Upper bound limit analysis of meso-mechanical spandrel models for the pushover analysis of 2D masonry frames

In this paper, a numerical model for the pushover analysis of in-plane loaded unreinforced masonry walls is presented. For the analysis of the walls, which consist of vertical piers connected by horizontal masonry spandrels, an equivalent frame model is adopted. The analysis approach consists of two steps: In Step I, ultimate bending moment-shear force strength domains of the masonry spandrels are derived by means of a heterogeneous upper bound FE limit analysis and the results are stored in a database. Assessing the capacity of the spandrels correctly is crucial for the ultimate resistance of masonry walls that are loaded in-plane. Heterogeneous limit analysis is particularly suitable for computing the failure load of unreinforced masonry members since it permits a distinct modelling of bricks and mortar joints. Appropriate static and kinematic boundary conditions are imposed to account for the complex interaction of internal forces and deformed shapes of the spandrel beams at failure. In Step II, a frame model of the masonry wall is assembled. In this frame model the spandrels are modelled as elastic Timoshenko beams. At each analysis step it is checked that the internal forces of these coupling beams are smaller than the failure loads stored in the database created in Step I. If the capacity is exceeded, flexural hinges are introduced at both ends of the coupling beam. The resistance of the element is set to zero when a limit chord rotation is exceeded. The piers are modelled in a similar manner. The shear force and bending moment capacity of the piers are, however, simply estimated according to the Italian Design Code. Pushover analysis results compare favourably with computationally expensive 2D nonlinear heterogeneous FE analyses, but also confirm that the ultimate lateral resistance of masonry walls is very sensitive to the assumed spandrel strength if an equivalent frame model is used.

Exterior wide beam–column connections in existing RC frames subjected to lateral earthquake loads

In this paper, the seismic performance of reinforced concrete exterior wide beam–column connections with shallow spandrel beams lightly reinforced for torsion and moderate levels of gravity loads was investigated experimentally. The study focuses on existing frames designed and detailed according to construction practices used over ten years ago in the moderate-seismicity Mediterranean area. The results can be useful for assessing the seismic vulnerability of older structures and orienting seismic retrofit alternatives. Two 3/5 scale test models representative of exterior sub-assemblages in a prototype six-story building were subjected to gravity-load levels typical of those acting during an earthquake, and quasi-static cyclic lateral loads until failure. The performance was studied in terms of strength, displacement, ductility and energy dissipation capacity. The data are analyzed in conjunction with the results of previous tests. The specimens exhibited a “strong column–weak beam” type of flexural yielding mechanism. The average drift ratios at first yielding of the wide beam longitudinal reinforcement, δ y o , and at failure, δ u , were 2.2% and 4.5% respectively; the displacement ductility ratio μ was approximately 2.2. Comparison to similar connections without added gravity loads showed that moderate levels of gravity loading increased δ y o by about 40%, and decreased by a similar percentage the value of μ and the energy dissipated in each half cycle of displacement expressed in terms of an equivalent viscous damping ratio. Finally, two approaches for estimating the wide-beam flexural capacity are examined.

Floor System Evaluation of a Riveted Steel Arch Bridge

The Omega Bridge is a riveted, steel arch bridge built in the early 1950s to cross the Los Alamos Canyon and connect the town of Los Alamos, New Mexico to technical areas of the Los Alamos National Laboratory. The alternate route from the bridge runs through the canyon on a steep grade, which is not a suitable option, particularly for emergency vehicles such as fire trucks. In the early 1990s, the bridge was rehabilitated due to the poor condition of the deck and increased traffic demands, which resulted in several changes to the original structure. This paper discusses the load rating of the bridge as affected by the rehabilitation according to the AASHTO load factor rating method. Attention is given to the evaluation of the floor system components including the stringers, floor beams, and spandrel beams. It is shown that the Omega Bridge is in satisfactory structural condition, no load posting is necessary, and the bridge is safe for the passing of emergency response vehicles.

Experimental Investigation on Seismic Behavior of Eccentric Reinforced Concrete Beam-Column-Slab Connections

This paper seeks to supplement existing information on the seismic behavior of eccentric connections by presenting an experimental study that focused on the effect of eccentricity of spandrel beams with respect to the column. Specimens included a floor slab and transverse beams to evaluate the effect of slab participation. Test results indicated that including the floor system significantly reduced the negative influence of eccentricity. Damage was reduced, specimens had fuller load-versus-drift hysteresis loops with high energy dissipation capacities, and deterioration of joint shear stiffness and strength were delayed. The joint shear stresses resisted by the connections, without major damage, also were higher than current design values due to the participation of a larger area of the joint region in resisting shear. These findings indicate that current ACI-ASCE recommendations for effective joint width of beam-column connections in monolithic reinforced concrete structures are conservative. Since joint shear distortions contributed significantly to the total story drift for all subassemblies, accurately predicting drift demands requires a joint model that accounts for the inelastic deformations in the beam-column connections.

Case study using the Los Angeles tall buildings structural design council guidelines: 40‐storey concrete core wall building

AbstractLos Angeles Tall Building Design Council (LATBDC) 2005 guidelines for analysis and design of tall buildings are utilized for the design of a 40 storey tall reinforced concrete building located in downtown Los Angeles. The case study structure is a 415 feet tall reinforced concrete residential building with 118 feet by 96 feet plan area. Lateral load carrying system of the building is bearing walls coupled with 32 to 60 inches deep spandrel beams. Gravity system consists of 8″ thick post‐tensioned concrete flat slabs resting on reinforced concrete gravity columns and bearing walls. Linear and nonlinear dynamic analysis procedures were followed using 475 and 2,475 year return period seismic events respectively. Design of core wall segments and spandrel beams connecting the segments together were controlled by both of these seismic hazard levels and analysis procedures. Nonlinear dynamic analysis of the 40 storey building showed inelastic flexural response at the spandrel beams over the building height in addition to the first few levels of the core wall segments. As intended, recorded component deformations were within the collapse prevention performance limits set by FEMA 356. The case study results highlight a significant limitation for Step 2 (Life Safety for DBE) to demonstrate achievement of ‘life safety’. Copyright © 2007 John Wiley & Sons, Ltd.

Finite Element Study of Shear Behavior of Spandrel Ledges and Comparison with PCI Shear Design Provisions

Punching shear failure of spandrel ledges has been observed by many researchers and heightened concerns have been raised questioning the safety level of the PCI shear design provisions for beam ledges. This paper presents non-linear finite element analyses conducted to model the behavior of prestressed L-shaped spandrel beams. Special emphasis was given to the behavior of the ledge at the end regions of the spandrel, where punching shear controls the design. The accuracy of the finite element model is demonstrated by comparing the predicted behavior to the results of one major test by another researcher. The influence of different parameters included in the PCI shear design provisions for beam ledges is discussed. The analysis is extended to illustrate the effect of other parameters including the prestressing level, hanger reinforcement and the amount of debonded strands at the end regions of the spandrel beam. Results of the analyses showed that the PCI shear design provisions for spandrel ledges are dangerously unconservative. The provisions do not account for key parameters, which affect the punching shear behavior.

Seismic Behavior of RC Wide Beam-Column Connections Under Dynamic Loading

In this article, the seismic behavior of RC wide beam-column connections designed primarily for gravity loads is evaluated experimentally. A 2/3 scale model of one exterior and one interior connection is constructed and subjected to seismic simulations on a shaking table until collapse. The results of the tests indicate that: (a) the drift at yield is from 3 to 6 times higher than, for example, the 0.5% admitted by Eurocode 8 to satisfy the “damage limitation requirement;” (b) the beam-column joints do not fail; (c) the torsion in the spandrel beams governs the overall load-displacement relationship of the exterior connections and limits the ultimate strength. Based on the test results, a nonlinear model for predicting the hysteretic behavior and the failure of the connections is suggested. The model can be implemented in a computer code for evaluating the vulnerability of this type of structure through nonlinear dynamic response analyses.

Compatibility Torsion in Spandrel Beams Using Modified Compression Field Theory

The authors present a procedure created to calculate the compatibility torsion in spandrel beams and other indeterminate structures. The Modified Compression Field Theory (MCFT) is relied upon to calculate cracked torsional and flexural stiffness for sections subjected to various combinations of stress resultants. Comparisons are made for the calculated ultimate loads to experimentally observed ultimate loads of statically indeterminate floor beam-spandrel beam frames. The comparison demonstrates that the MCFT is able to calculate the response of reinforced concrete sections subjected to combined shear, torsion, bending moment, and axial compression. Additional conclusions reveal that where the effects of compatibility torsion are dominant, the proposed procedure is capable of predicting the response of indeterminate frames.

Design for Torsion and Shear in Prestressed Concrete Flexural Members

This paper presents a unified method for the torsion and shear design of prestressed and non-prestressed concrete flexural members, and provides an alternative method to the provisions of the ACI Building Code. The method applies to rectangular, box and flanged sections such as L-beams. The approach depends on subdividing the given section into component rectangles. Equations are given for the shear and torsion web reinforcement of beams as well as expressions for the minimum reinforcement and required amount of longitudinal steel. The design method is illustrated with a fully worked numerical example of a spandrel beam. The shear and torsion provisions in the Sixth Edition of the PCI Design Handbook are based on the principles outlined in this paper, which will also be referenced in ACI 318-05. The design method has been shown to be reliable, accurate and easy to use.

Torsional Strengthening of Spandrel Beams with Fiber-Reinforced Polymer Laminates

Research has shown that fiber-reinforced polymer (FRP) composites can increase flexural, axial, and shear capacity of beams, columns, and walls. The present paper describes both experimental and analytical programs focused on the torsional strengthening of reinforced concrete spandrel beams using composite laminates. The variables considered in this study included fiber orientation, composite laminate, and effects of a laminate anchoring system. The study proved that the FRP laminates could increase the torsional capacity of concrete beams by more than 70%. The analytical procedure developed revealed a good comparison between experimental and analytical results.

Torsional retrofit of spandrel beams with composite laminates

This paper describes the experimental and analytical findings of a project focused on the structural strengthening of reinforced concrete (RC) spandrel beams using carbon fibre reinforced polymer (CFRP) composite laminates, and subjected to pure torsion. Many current torsional strengthening and repair methods are time and resource intensive and quite often very intrusive. The proposed method, however, uses composite laminates to increase the torsional capacity of concrete beams. In traditional cast-in-place construction, the slab adjacent to the spandrel beam does not allow a complete CFRP wrap around the beam. To simulate this condition, the CFRP laminate was provided only on three sides of the beam, and special anchors were used to allow a continuous torsional shear flow around the specimens. The experiments showed that this method increased the torsional strength of the spandrel beams by up to 77%. Excessive concrete cracking followed by composite delamination caused the specimen failures. An equation was developed that, for most of the specimens, accurately predicted the composite contribution. This analytical procedure was based on the existing information on the torsional resistance provided by closed stirrups, and on the equations developed to design the composite shear retrofit of RC beams.