Journal of Structural Engineering

Upon recent research, steel plate shear wall (SPSW) is known as an effective lateral force resisting system in high seismic zones. However, there are still areas of concern in the design and construction of this system with regard to conventional approaches recognized as stiffened and unstiffened types. This paper presents results of research conducted on diagonally stiffened steel plate shear walls as a new type of stiffening method. Four $1/2$-scaled single-story test specimens are designed as prototype thin steel plate shear walls for the experimental study. Three of the specimens are diagonally stiffened, and the fourth one is an unstiffened steel shear wall. Testing of the systems is performed under cyclic quasi-static loading. The effects of the edge stiffeners and the type of beam-to-column connections on the seismic behavior of the diagonally stiffened specimens are also investigated. Experimental results show that the specimens tolerate 3.5% to approximately 5% story drifts, and the diagonal stiffeners improve hysteretic behavior of the steel shear walls, especially when the edge stiffeners are used in the panel. The results indicate that the response modification factor ($R$) of a diagonally stiffened specimen is approximately 13% greater than the $R$ factor of an unstiffened system. In addition, a formula is developed and proposed for the shear strength estimation of a diagonally stiffened SPSW. The theoretical predictions of the shear strengths are compared with the experimental results, and good agreements are observed between the two methods.

Large-scale shake table tests were performed at E-Defense to examine the out-of-plane stability of buckling-restrained braces (BRBs). Two specimens were subjected repeatedly to a near-fault ground motion with increasing amplification. The test specimens comprised a single-bay, single-story steel frame and a pair of BRBs placed in a chevron arrangement. The specimens were not braced at the brace-to-beam intersection in order to produce a condition where the BRBs were susceptible to out-of-plane instability. Standard BRBs were used in the first specimen, while BRBs with a flexible segment at each end of the steel core were used in the second specimen. A simple stability model predicted the BRBs in the second specimen to fail because of out-of-plane buckling. The first specimen exhibited excellent ductility during the shake table tests, while the second specimen developed severe out-of-plane deformation that compromised the ductility of the BRBs. Based on the experimental observations and the stability model, a methodology is proposed to evaluate bracing requirements at the brace-to-beam intersection.

The behavior of a self-centering moment-resisting frame (SC-MRF) is characterized by the connection gap opening and closing at beam-column interfaces under earthquake loading. A SC-MRF uses high-strength posttensioning strands to precompress the beams to the columns and to close the gaps that develop under earthquake loading, returning the frame to its initial position (i.e., the frame is self-centering). In this study, a beam web friction device is included in each beam-column connection to dissipate energy under seismic loading. Unlike a special steel moment-resisting frame with welded connections (W-SMRF), a SC-MRF can be designed to survive the design basis earthquake (DBE) without structural damage, leading to the potential for immediate occupancy performance, and to suffer only modest damage under the maximum considered earthquake, leading to collapse prevention performance. A 7-bay, 4-story SC-MRF prototype building was designed for a location in the Los Angeles area. A 0.6-scale model of two bays of the SC-MRF building was constructed in the laboratory and subjected to simulated earthquakes using the hybrid simulation method. This paper focuses on the DBE-level performance of this SC-MRF. DBE-level simulation results and performance evaluations are presented. The behavior of the SC-MRF is compared with that of a W-SMRF using nonlinear pushover analysis results.

The behavior of extended end-plate connections with a circular bolt pattern under static and cyclic loads is investigated. Twelve three-dimensional numerical models were developed and analyzed using the FEM, and the results of the connections with a circular bolt pattern were compared with those with a traditional square bolt pattern. The effects of various bolt diameters and end-plate thicknesses on the bolt-force distribution of each bolt pattern are investigated. The results of this study showed that the circular bolt pattern can enhance the moment capacity, reduce pinching, and ultimately increase the energy dissipation of the connections depending on their geometric parameters.

Plain C- or Z-sections are two of the most common cold-formed steel shapes in use throughout the world. Other shapes are high-strength SupaCee and SupaZed (Bluescope Steel Ltd., Melbourne, Australia) steel sections, which are widely used in Australia as purlins in roof and wall systems. They contain additional return lips and web stiffeners that enhance the bending capacity of the sections. Design methods for these sections are normally specified in the Australian/New Zealand Standard for cold-formed steel structures or the North American Specification for cold-formed steel structural members. In both standards, which include the newly developed direct strength method of design (DSM), the method presented is developed for beams and columns, including the reliability of the method. This paper presents two different test series on both plain C- and SupaCee sections in pure bending (constant moment). They were performed at the University of Sydney for the extension of the DSM to include channel section beams with complex stiffeners. Two different section depths and three different thicknesses of high-strength lipped channel sections were tested in pure bending. Tests with and without torsion/distortion restraint straps screwed on the top flanges in the pure bending region were also considered to allow local and distortional buckling to form in the sections, respectively. Test results and formulas developed from the DSM are summarized in the paper. Three different cases where moments are used in association with yield, inelastic, or plastic criteria in the DSM local and distortional strength equations are compared with the test data. By comparisons between cases, a proposed recommendation for DSM inelastic buckling strength design in pure bending with extended nondimensional slenderness limit for both local and distortional buckling is given in the paper.

At ambient temperature, estimations of the postbuckling strength of steel plates (web and flanges) in wide-flange beams are based on the assumption that the stress at the edge of the plate equals the yield stress of the material. However, at elevated temperatures material behaves in a nonlinear manner beginning at very small strains. The work presented in this paper has shown that at elevated temperatures the ultimate buckling load occurs when stresses at the plate edge are smaller than the yield stress, which are typically defined at large strains such as at 2%. Hence, the current expressions for plate buckling strength at ambient temperature cannot be directly applied at elevated temperature. By taking into account the nonlinear behavior of steel at elevated temperatures, a new postbuckling strength equation for webs and flanges in wide-flange beams that correlates well with finite-element studies at elevated temperatures is proposed.

Nodal T-connections made up of circular hollow section (CHS) braces and square hollow section (SHS) chords (CHS-SHS T-connections) have the advantage that they do not require complex brace end preparation when compared with CHS-CHS T-connections. The stress-concentration factors (SCFs) in CHS-SHS T-connections have also been found to be lower than those in SHS-SHS T-connections by previous researchers. At present, no parametric equations have been developed for determination of SCFs for the design of CHS-SHS T-connections. In this investigation, eight CHS-SHS T-connections with unique nondimensional parameters were strain gauged for determination of strain-concentration factors (SNCFs) and therefore SCFs. A three-dimensional finite-element model was then developed using the ANSYS software to simulate the stress distribution at the brace-chord welded interface under axial force and in-plane bending in the brace. Validation of the model was carried out by comparing the SNCFs determined from the experiment and those determined from the finite-element model. It was found that the finite-element models were able to capture both the maximum SNCF in the connection and the SNCF distribution around the brace-chord welded interface. A parametric study was carried out to determine the SCFs for numerous models with unique nondimensional parameters $\beta \hspace{0.17em}(=d_1/b_0)$, $2\gamma \hspace{0.17em}(=b_0/t_0)$, and $\tau \hspace{0.17em}(=t_1/t_0)$. Using multiple regression analysis, equations have been developed for SCFs at hot spots around the CHS-SHS T-connections under the loads axial force in the brace and in-plane bending in the brace. There is good agreement between the maximum SCFs in the CHS-SHS T-connections calculated by the resulting formulas and the maximum experimental SCFs in the connections.

AASHTO LRFD and AISC specifications have adopted Basler’s interaction equation, which was formulated for noncompact sections without considering shear buckling. AASHTO LRFD specifications, however, have completely neglected the interaction effect of bending on shear strength since the 3rd edition in 2004. AISC LRFD specifications followed suit with the 2005 edition. This study was aimed at investigating interaction behaviors in noncomposite I-girders and developing new interaction equations without considering shear buckling. Also, a simple and universally applicable methodology was proposed for web panels whose failures were associated with shear buckling. The interaction should not be ignored when web failures are governed by yielding because of combined bending and shear. Otherwise, the shear capacity of the web panel could be grossly overestimated, thereby compromising the safety of the girder.

The requirements for the anchorage of beam longitudinal reinforcement at interior beam-column joints in earthquake-resistant RC moment-resisting frames are reevaluated. An introductory comparison of international design criteria shows that a broad disparity currently exists between these requirements. The suitability of existing criteria was assessed by assembling a database of more than 90 interior beam-column joint tests and comparing the assessed test performance with the performance that was predicted by each design criterion. This comparison showed that none of the existing design criteria were adequately able to predict experimental performance. To improve the design of earthquake-resistant RC frame structures, an improved design criterion was developed by parametrically determining the influence of important variables on anchorage performance.

It is necessary to predict the plastic deformation demand of members and the story drift ratio for seismic design. In the present study, a simple method of estimating the plastic rotation of beams in special steel moment-resisting frame structures designed by the strong column-weak beam philosophy was developed. The plastic rotation of beams was calculated as the function of the story drift ratio based on the result of elastic analysis. The effects of the design parameters, such as moment redistribution, joint dimension, plastic mechanism, panel zone deformation, and the rocking effect of lateral bracing were addressed. For verification, the proposed method was applied to 6-story special moment frames with and/or without lateral bracing. The plastic rotations of beams in the same floor significantly varied according to the design parameters, although the story drift ratio was the same. The plastic rotations of beams predicted by the proposed method correlated well with those from nonlinear static analysis.

This paper discusses the lateral load behavior of two, 0.40-scale, hybrid, precast concrete shear wall test specimens and the behavior of a third precast specimen designed to emulate monolithic cast-in-place RC shear walls. The walls had identical overall geometry and were constructed by placing rectangular precast panels across horizontal joints. The hybrid walls used mild steel bars [Grade 400 (U.S. Grade 60)] and high-strength unbonded posttensioning (PT) strands for lateral resistance, whereas the emulative wall used only mild steel bars. The mild steel bars crossing the base joint were designed to yield and provide energy dissipation, with the PT steel in the hybrid walls reducing the residual displacements of the structure. The mild steel bars at the base of the emulative wall and one of the hybrid walls used Type II mechanical splices, while the other hybrid wall used continuous bars grouted into the foundation. Because of the lack of PT steel, the emulative wall developed a large residual uplift at the base joint, resulting in excessive horizontal slip and strength degradation. The behavior of the hybrid wall with Type II splices was also limited, which occurred because of the pullout of the mild steel bars. In contrast, the hybrid wall with continuous mild steel bars showed superior restoring, energy dissipation, and ductile behavior over larger lateral displacements. The results show the potential for the use of precast walls in seismic regions, while also revealing important detailing considerations.

An analytical study is performed to evaluate the effect of shear wall area to floor area ratio on the seismic behavior of midrise RC structures. For this purpose, 24 midrise building models that have five and eight stories and shear wall ratios ranging between 0.51 and 2.17% in both directions are generated. Then, the behavior of these building models under earthquake loading is examined by carrying out nonlinear time history analyses. In the analyses, seven different ground motion records are applied to the building models, and the average of the obtained data is used in the evaluation of the seismic performance. Main parameters considered in this study that affect the overall seismic performance of the buildings are the roof and interstory drifts and the base shear responses. The analytical results indicate that at least 1.0% shear wall ratio should be provided in the design of midrise buildings to control the drift. In addition, when the shear wall ratio increases beyond 1.5%, it is observed that the improvement of the seismic performance is not as significant.

This study was organized to derive an analytical expression for the estimation of plastic hinge length for cantilever structural walls using the results of comprehensive nonlinear finite-element analyses. For that purpose, a parametric study was conducted. The variation of plastic zone length at the base of the cantilever shear wall models was determined on the basis of analysis results that depend on several parameters, such as the wall length, wall height, axial load ratio, and the ratio of wall boundary element and the web horizontal reinforcement. In light of the parametric investigation, a plastic hinge length expression was proposed dependent on wall length, axial load ratio, wall horizontal web reinforcement ratio, and shear-span-to-wall-length ratio. Existing plastic hinge length prediction formulations were also compared with the plastic hinge length obtained from finite-element analyses. Finally, the accuracy and reliability of the proposed plastic hinge length equation was verified by using the available shear wall test results.

Despite extensive investigations of bond stress versus slip modeling for RC structures, most existing bond stress–slip models are incomplete, discontinuous, and insufficiently accurate. These problems can cause nonconvergence and other difficulties in computational simulations of concrete structures that use bond-slip models. Through systematical analyses of an existing database of bond-slip behavior and data regressions, this work develops a unified bond stress–slip model that overcomes these difficulties and is suitable for numerical simulations. The model is given by a single and mathematically continuous equation that does not distinguish between plain and confined concrete or splitting and pullout failure because such judgments are arrived at automatically by evaluating the model parameters. Furthermore, the model outperforms the existing models in the precision of its predictions.

To expand the scope of accurate and efficient gradient-based applications in structural engineering, the direct differentiation method (DDM) is applied to compute the response sensitivity of force-based frame finite elements with combined material and geometric nonlinearity where the transverse displacement field is determined by curvature-based displacement interpolation. Sensitivity is developed for element-level parameters including constitutive properties, cross-section dimensions, and integration points and weights, as well as structural-level parameters corresponding to nodal coordinates. The response sensitivity is found to be significantly more complicated than for geometrically linear force-based elements because it requires the derivative of the transverse displacement field under the condition of fixed basic forces. Finite-difference calculations verify the DDM sensitivity equations for material and geometric nonlinear force-based element response while reliability analysis of a gravity-loaded steel frame demonstrates the efficiency of the DDM sensitivity in a gradient-based application.

The lateral deformation behavior of a RC column is particularly important because it not only magnifies the moment but also affects the ability of the column—and, subsequently, the frame—to sway and absorb energy at all stages of loading. The lateral deformation is affected by disturbed regions, such as tensile cracks or compression wedges, which are often simulated with the help of hinges whose properties are derived empirically. Being empirical, these hinges can only be used within the bounds of the tests from which they were derived, and in this respect are of limited use. In this paper, a mechanics-based hinge is developed that can be used at all stages of loading (that is, at serviceability through to ultimate) and also during failure. The mechanics-based model is based on the principle of plane sections remaining plane, shear-friction theory that quantifies the behavior of RC across sliding planes, and partial-interaction theory that allows for slip between the reinforcement and the encasing concrete. Being mechanics based, it can be used for any type of RC column; that is, for any type of reinforcement and for any type of concrete as long as the material properties are known. The mechanics model is shown to be in good agreement with published test results and can simulate not only multiple cracks if necessary but also the formation of wedges.

Rock-concert events in stadiums have raised complaints among dwellers of neighborhood buildings about annoying vibrations in Buenos Aires, Argentina, Wellington, New Zealand, Medellín, Colombia, and other cities around the world. Controversy about the causes and effects of vibrations has produced demands, alarms among inhabitants, and cancellations of spectacles with large economic consequences. Although the analysis and effects of vibrations on the stadium grandstands are well known, no comprehensive published paper could be found that addressed the effects of vibrations on neighborhood buildings when thousands of spectators jump on a stadium field. This paper covers this gap in civil engineering knowledge, introducing a systematic study (analytical and experimental) to explain the causes, predict building responses, and determine the size of the expected human, structural, and cosmetic effects on neighborhood buildings. First, the equations for modeling are presented: (1) the coordinated jump of the public on the field and the load generated, (2) the acceleration-wave propagation over the surface of an elastic solid, and (3) the responses of buildings at different distances from the stadium. The resulting equations are used to estimate the accelerations at building tops at distances within a radius of 3 km of the stadium. Second, the measurements planned and obtained during concerts are shown and evaluated. The results indicate that for buildings in resonance with the spectators’ jumps (natural frequency of 2.1 Hz for 10- to 12-story buildings in Buenos Aires), the acceleration level in the upper stories is severe to people at distances of more than 3 km from the stadium, but it is not high enough to cause structural or nonstructural damage.

Cold-formed steel stud walls are an attractive alternative to wooden stud walls because of their ductility, sustainability, and resistance to insects, mold, and rot. To date, engineers have faced challenges using steel stud walls to mitigate blast loads because of strict response limits set forth by existing standards that address blast-resistant design. Because of the limited past research on the response of steel stud walls subject to blasts, uncertainties exist regarding how these systems transition from elastic to inelastic response, particularly when lateral torsional buckling or local buckling of a section occurs. Existing standards used to design structures to mitigate blast loads penalize the use of steel stud walls by incorporating large safety factors that make the design of these systems uneconomical, which prevents engineers from taking full advantage of their benefits. The goal of the research described in this paper is to evaluate the suitability of conventional construction techniques to design and build steel stud walls that are capable of resisting blast effects associated with common threat scenarios. The work carried out to meet this goal included four controlled series of laboratory experiments. Results from this study demonstrate that the overall stiffness and strength of steel stud walls can be significantly greater than the values currently indicated in available design guidelines and that steel stud walls can be utilized to resist blast threats using conventional construction methods that add little cost to traditional designs.

In Portugal, given the large proportions of natural regeneration pine stands, a large amount of young trees must be removed from the forest, to assure the quality of mature trees and to decrease the risk of fire. With this problem in mind, a national study was launched to investigate the use of maritime pine small-diameter poles in structural applications. The study had two different tasks. The first task comprised the determination of mechanical properties and the establishment of visual and mechanical strength grading procedures and is already completed. The second task concerns the development of connections. This paper presents results within the second task. Three types of connections, regarding failure load and stiffness, were studied: connections using central plates; glued-in rods; and dowel nuts. The glued-in rods showed the highest mean failure load and, especially, stiffness. Indeed, the glued-in rods showed a mean stiffness around six times higher than the one obtained for the other studied connections. Additionally, the applicability of European Yield Model to estimate the failure load of these connections is also discussed.

The material presented in this paper refers to a part of the investigation on cross-laminated (XLam) wall panel systems subjected to seismic excitation, carried out within the bilateral project realized by the Institute of Earthquake Engineering and Engineering Seismology (IZIIS) and the Faculty of Civil and Geodetic Engineering at the University of Ljubljana (UL FCGE). The full program of the research consists of basic tests of small XLam wooden blocks and quasi-static tests of anchors, then quasi-static tests of full-scale wall panels with given anchors, shaking-table tests of two types of XLam systems including ambient-vibration tests, and finally analytical research for the definition of the computational model for the analysis of these structural systems. In this paper, the full-scale shaking-table tests for one XLam system type (i.e., specimen 1 consisting of two single-unit massive wooden XLam panels) that have been performed in the IZIIS laboratory are discussed. The principal objectives of the shaking-table tests have been to get an insight into the behavior of the investigated XLam panel systems under seismic excitations, develop a physical and practical computational model for simulation of the dynamic response based on the tests, and finally correlate the results with those from the previously performed quasi-static tests on the same wooden panel types. The obtained experimental results have been verified using a proposed computational model that included new constitutive relationships for anchors and contact zones between panels and foundations. Because a reasonable agreement between the numerical and experimental results has been achieved, the proposed computational model is expected to provide a solid basis for future research on the practical design of these relatively new materials and systems.

Laboratory tests were used to quantify the effects of section shape, screw density, and polyurethane adhesive use on laminated wood assembly bending strength and stiffness. Both I-shaped sections and vertically laminated rectangular sections were studied, each utilizing three $38\times 140\text{-}\text{mm}$ members. I-sections featured dimension lumber flanges screwed to laminated strand lumber (LSL) webs. In half of these assemblies, polyurethane adhesive was used in addition to screws. Only screws and dimension lumber (no LSL or adhesive) were used in fabrication of the vertically laminated assemblies. Bending strength and stiffness were significantly increased by the reconfiguration of members into an I shape. Composite action, and therefore bending strength and stiffness, was significantly increased by the addition of polyurethane adhesive to I-sections. This research presents an efficient assembly design with bending strength and stiffness values significantly higher than those of the current industry standard mechanically laminated assembly.

This paper presents a study aimed to determine the cyclic performance of wood-frame shear walls sheathed with glued laminated Guadua bamboo (GLG) panels as a first step to evaluate their potential application. GLG-sheathed walls having 2:1 and 1:1 aspect ratios and three different sheathing nail spacing were tested under cyclic conditions. Parameters, such as peak shear strength, shear modulus, displacement ductility demand, and energy dissipation of the walls, were examined. Values for peak shear strength were then compared with those of walls sheathed with wood or wood-based panels. The wall aspect ratio was found to be a parameter with lesser impact than nail spacing. It was also found that the reduction in nail spacing increases to some extent the strength, stiffness, and energy dissipation, but lowers the ductility of the wall. The peak cyclic shear strength of shear walls sheathed with GLG panels was found to be within the shear strength reported for wood or wood-based panels and the tested oriented strand board and plywood control specimens. Higher specific gravity of GLG panels compared with wood-based panels has a positive effect in avoiding tearing and pull-through failures of the panel and leads to higher energy dissipation of the wall. Based on test results, GLG panels could be a suitable structural replacement of wood or wood-based panels used in wood-frame construction.

Shaking table tests of two 1:2 scale prototype structures were performed to study the seismic performance of Chinese traditional wood structures and light wood-framed structures. The results show that the natural frequency (2.18 Hz) of the Chinese traditional wood structure (CTWS) in the lateral direction is less than that of the light wood-framed structure (LWFS), equal to 5.34 Hz, which indicates that the lateral stiffness of the CTWS is less than that of the LWFS. When the peak value of acceleration input (PAI) is less than 0.5g, the lateral acceleration response at the roof of CTWS will be less than input; the dynamic magnification factor of acceleration ranged from 0.46 to 0.57. Furthermore, for a PAI greater than 0.2g, the obvious slippage between the columns and base stones, as well as the deformation of joints connecting beams with columns, is evident in CTWS. This behavior allows for dissipation of earthquake energy. However, for LWTS, when the PAI is greater than 0.4g, the dynamic magnification factor of acceleration will be more than 1.0, meaning that the effect of diminishing acceleration response of CTWS is better than that of LWTS. If the PAI is less than 0.5g, the LWFS retains elastic, meaning that the seismic performance of the LWFS is superior to that of the CTWS with the same plan. In summary, the models and prototype structures can provide life safe performance when the design earthquake ground motion is equal to 0.20g and meet collapse prevention performance when the maximum considered earthquake ground motion is equal to 0.40g.

The purpose of this paper is to discuss issues associated with ASCE 7-10 standard methods for determining wind loads on buildings and other structures that warrant comment, correction, or improvement. The assessment is intended to serve as a resource in the development of a new version of the ASCE 7 standard and to stimulate a wider participation in that development by the structural engineering community. Issues discussed in the paper include: wind speeds in nonhurricane regions; alternative analytical methods for determining wind loads and wind effects on main wind force resisting systems and components and/or cladding; aerodynamic pressure coefficients; pressures on rooftop equipment; component and cladding pressures on arched roofs; and the wind tunnel procedure. It is noted that the ASCE 49 standard essentially covers wind tunnel testing, rather than the wind tunnel procedure, of which wind tunnel testing is only a part.