Journal of Structural Engineering

Development in ultra-high-performance fiber-reinforced concrete (UHPFRC) structural applications that has taken place over the last two decades has generated innovative concepts that could significantly impact the concrete construction practice. The transition from conventional concrete with brittle behavior to strain-hardening behavior in direct tension allows consideration of the design of innovative structural components and offers development of new techniques for rehabilitation. Building on experimental results of internally instrumented reinforcing bars, this paper investigates the impact of tensile characteristics of UHPFRC on the performance of lap splice connections using a refined three-dimensional (3D) finite-element (FE) model at rib scale and a 3D concrete constitutive model implemented in a computer program. The results show that the model reproduces with accuracy the experimental behavior of lap splice connections in UHPFRC in terms of maximum strength, splitting failure mode, crack pattern, steel stress distribution along the splice, and eventual loss of bond. Using the validated 3D nonlinear finite-element model, the influence of splice length and UHPFRC cover thickness are highlighted in a parametric study of corner and interior lap splices. The paper illustrates the methodology that can be adopted along with experimental results to develop guidelines for designing lap splice connection in UHPFRC.

Prestressed (PS) strands are widely used to develop prestressed concrete (PSC) and are stronger than other types of structural steel used in the construction industry. Because of their high strength, PS strands are more effective for use in structures than other materials. Recently, high-strength 2,400-MPa PS strands have been developed and are being considered as an alternative to conventional 1,860-MPa PS strands. However, there have been no reports of research or proposed regulations for pretensioned 2,400-MPa strands in PSC. In this study, 28 PSC beams were fabricated by using 2,400-MPa PS strands, and the transfer length of the PSC was measured. Experiments were performed to evaluate several parameters such as the compressive strength of concrete, steel–fiber volume ratio, and stirrup reinforcement along with different de-tensioning methods in order to determine their effects on the transfer length. In addition, the transfer length with the 2,400-MPa PS strands was measured and compared with the transfer length predicted by previously proposed models.

In this paper, a new approach for estimating the probability of failure is proposed. The method works by dividing the input space into subspaces with the Voronoi diagram and applying the unscented transformation in each subspace. The probability of failure is defined as the sum of the products of the expectation of the failure domain indicator function and the corresponding weight in subspaces. A small number of samples is needed for this method to get a failure probability estimation with high accuracy. The efficiency and robustness of the proposed method are investigated by solving several examples. The results are compared with results of other reliability methods, and they demonstrate the efficiency and robustness of the proposed method.

Topology optimization can be divided into continuum and discrete types, the latter being the emphasis of the present work. In the field of discrete structural topology optimization of trusses, the generation of an initial ground structure is crucial. Thus, this paper examines the generation of ground structures for generic structural domains in two and three dimensions. It compares two methods of discretization, Voronoi-based and structured quadrilateral discretizations, and proposes two simple and effective ground structure generation approaches: the macroelement and macropatch approaches. Both can be implemented with either type of discretization. This work presents several features of these approaches, including the efficient generation of initial ground structures, a reduction in matrix bandwidth for the global stiffness matrix, finer control of bar connectivity, and a reduction in the number of overlapped bars. Generic examples and practical structural engineering designs are presented. They display the features of the proposed approaches and highlight the comparison with results from either the literature, the traditional ground structure generation, or the continuum optimization method.

This paper presents a comprehensive experimental study of the buckling behavior of ferritic stainless steel tubular section beam-column structural members subjected to unequal end moments. Testing was carried out on two cold-formed and seam-welded cross sections—one rectangular hollow section (RHS) $100\times 40\times 2$ and one square hollow section (SHS) $60\times 60\times 3$ made of grade AISI 410 (EN 1.4003) stainless steel. The experimental investigation included a series of material tensile coupon tests, initial local and global geometric imperfection measurements and 24 beam-column tests under unequal end moments. The experimental setup and procedures are described, and the test observations, including the key test results, the load-deformation histories, and the failure modes, are fully reported. The experimental results were carefully analyzed and then compared with the design strength predictions determined according to the current European code, American specification, and Australian/New Zealand standard for stainless steel structures, enabling the accuracy of each codified method to be evaluated. Generally, the European code resulted in the most conservative and scattered strength predictions among the three codified approaches, owing principally to the use of the same treatment for stainless steel beam-columns under both equal and unequal end moments. The American specification and Australian/New Zealand standard employ an equivalent uniform moment factor to consider the beneficial effects of moment gradient on beam-column strengths. These approaches were shown to offer more accurate and consistent capacity predictions for ferritic stainless steel beam-columns under unequal end moments, though further improvements remain possible.

Many coastal areas in the United States are subject to tsunami hazard. The public safety risk has been partially mitigated through warning and preparedness of evacuation, but community disaster resilience requires that critical and essential facilities provide structural resistance to collapse. Furthermore, there are coastal communities in the states of Alaska, Washington, Oregon, California, and Hawaii where there is insufficient time for evacuation. The Tsunami Loads and Effects Subcommittee of the ASCE/Structural Engineering Institute (ASCE/SEI) 7 Standards Committee has developed a new Chapter 6, titled “Tsunami Loads and Effects,” for the 2016 edition of the ASCE 7 standard Minimum Design Loads for Buildings and Other Structures (Minimum design loads for buildings and other structures). The new ASCE 7 provisions for tsunami loads and effects implements a unified set of analysis and design methodologies that are consistent with probabilistic hazard analysis, tsunami physics, and reliability analysis. The purpose of this paper is to provide analysis of the structural reliability basis for tsunami-resilient design of critical and essential facilities, taller building structures, and tsunami vertical evacuation refuge structures. Probabilistic limit-state reliabilities are computed for representative structural components carrying gravity and tsunami loads, utilizing statistical information on the key hydrodynamic loading parameters and resistance models with specified tsunami load combination factors. Through a parametric analysis performed using Monte Carlo simulation, it is shown that anticipated reliabilities for tsunami hydrodynamic loads meet the general intent of the ASCE 7 standard as stated in its Chapter 1 commentary. Importance factors consistent with the target reliabilities for extraordinary loads (such as seismic events) are determined for tsunami loads.

A tsunami is a series of great waves primarily caused by a major subduction-zone earthquake with large-scale displacement of the sea floor or by initiation of submarine landslides. Many coastal areas in the western United States are subject to tsunami hazard that is infrequent but potentially extremely destructive. The public safety risk has been only partially mitigated through warning and preparedness of evacuation; there are many coastal communities in the states of Alaska, Washington, Oregon, California, and Hawaii where there is insufficient time for complete evacuation, and places of higher elevation and/or taller structures could provide life safety. Community disaster resilience would also require that critical and essential facilities provide structural resistance to collapse. Towards that goal, the Tsunami Loads and Effects Subcommittee of the ASCE/Structural Engineering Institute (ASCE/SEI) 7 Standards Committee has developed a new Chapter 6 with design requirements for tsunami loads and effects, contained in the 2016 edition of the ASCE 7 standard Minimum Design Loads for Buildings and Other Structures [Minimum design loads for buildings and other structures]. The ASCE 7-16 “Tsunami Loads and Effects” chapter will become the first national, consensus-based standard for tsunami resilience for use in the states of Alaska, Washington, Oregon, California, and Hawaii. The purpose of this paper is to provide an explanation of the technical basis and methodology for tsunami-resilient design of critical and essential facilities, tsunami vertical evacuation refuge structures, and other multistory building structures. The ASCE 7 provisions for tsunami loads and effects implements a unified set of analysis and design methodologies with design maps based on probabilistic hazard analysis, loads based on tsunami physics, and a structural ultimate strength basis of design. Probabilistic offshore tsunami amplitude maps and tsunami design zone inundation maps were developed using a method consistent with probabilistic seismic hazard analysis in the treatment of seismic source uncertainties. Procedures for tsunami inundation analysis are based on using mapped values of offshore tsunami amplitude or the runup and inundation limit shown in tsunami design zone maps. The ASCE 7 “Tsunami Loads and Effects” chapter is consistent with the principles of probabilistic hazard analysis, tsunami physics, and fluid mechanics, integrated into a comprehensive set of design provisions.

The steel slit shear wall has attracted much attention as a lateral force-resisting system. However, issues such as fractures formed at the slit ends and pinched hysteresis reduce energy dissipation. To address these issues, the authors have developed a steel slit shear wall made from low yield point steel that has a low yield stress and large ductility and strain hardening. Steel slit shear walls made from low-yield-point steel dissipated energy at small lateral drifts, shear deformation was evenly distributed among all rows, fracture was eliminated, and fat hysteresis without the requirement for out-of-plane constraints was feasible. By adjusting dimensions of the link (segment divided by slits) and the number of rows of links while maintaining the required shear strength and stiffness, a small width-to-thickness ratio for the links was achievable to ensure the in-plane behavior of links and thus good energy dissipation. The combined hardening model developed using commercially available software simulated well the large strain hardening of low-yield-point steel. A proposed design procedure that ensures good energy dissipation was given.

Fiber-reinforced resin (FRR) plates are being incorporated into structural joints to correct thermal bridging issues to create more energy-efficient buildings. The purpose of this study was to evaluate the behaviors of simple shear and moment connections that include FRR thermal barrier plates under service-loading conditions. Tests included two thicknesses and two grades of barrier plate. The shear connection tests showed that the coefficient of friction between steel and an as-received FRR plate was significantly lower than that of steel on steel. However, roughening the FRR plates by blasting with aluminum oxide increased the coefficient to nearly the same as or greater than steel on steel. In moment connections the presence of thermal barrier plates increased the joint rotation at the connection. A 25-mm (1-in.) thermal barrier plate increased the joint rotation by 10% compared to a joint without the barrier plate. The increase was 20% for a 50-mm (2-in.) plate. The thermal barrier plates did not affect the dynamic response of the test fixture at structurally important frequencies.

A rocking spine system is introduced as an alternative to more conventional approaches to improve the seismic collapse safety of concrete frames with masonry infills. Although infill frames are not formally recognized in ASCE 7 or other current U.S. building codes for new buildings, infills are present in many existing buildings, and infill frames are still a prevalent type of new construction that is permitted in many parts of the world. The proposed technique uses structural spines, constructed using either strong infill panels or concrete walls, to resist earthquake effects through controlled rocking action. The primary sources of overturning resistance are gravity loads on the spine and the restraint provided by beams and infill panels in framing bays adjacent to the spine. Equations are developed to describe the rocking response of the spine, relating the rigid-body kinematics to the internal deformations, forces and limit states in beams, columns, and infill panels. The main aspects of the design method are presented, including guidelines for assessing and allocating the required overturning strength and for sizing and detailing key structural components to avoid undesirable failure mechanisms. The seismic design approach is illustrated for a six-story infill frame building, and nonlinear static and dynamic analyses are performed to evaluate its response. The analyses confirm the reliability of the simplified design procedures and demonstrate that the rocking spine system is effective in meeting drift limits in ASCE 7 and the collapse safety criteria of the FEMA P695 guidelines.

Wind characteristics in the atmospheric boundary layer (ABL) and structural performance under extreme wind conditions are of major concern in the design of tall buildings in tropical cyclone-prone regions. On August 22, 2008, Typhoon Nuri (0812) made landfall over Hong Kong and then passed over its city center. This paper presents the analyzed results of the observations collected at two offshore meteorological stations and by a structural health monitoring system installed in a 420-m-high supertall building in downtown Hong Kong during the entire passage of Typhoon Nuri. The wind characteristics over open (sea) and urban (city) terrains at different stages of the typhoon are presented and discussed. Moreover, the wind-induced responses of the supertall building during the typhoon are investigated. The structural dynamics properties and serviceability of the supertall building during a landfall typhoon are evaluated. This study aims to investigate the wind characteristics in the ABL during a landfall typhoon, and its impact on high-rise buildings in a metropolis so as to provide useful information for the wind-resistant design of supertall buildings in tropical cyclone-prone regions.

This study is concerned with the strength limit state of serial bolted connections in structural steel plates. It points out that the ultimate load capacity of a serial bolted connection failing in combined bearing and shear-out cannot be computed as the simple sum of the respective ultimate bearing and ultimate shear-out capacities, which is implicitly permitted in design specifications worldwide. Based on the laboratory test results of 10 hot-rolled steel plate specimens composed of three different grades with nominal thicknesses ranging from 5 to 8 mm, the paper first establishes the ultimate bearing coefficient of a 20-mm bolted connection in a structural steel plate to be 3.5. Coupled with the shear-out equation previously derived, a design equation where the shear-out capacity of the downstream bolt varying quadratically with the end distance is then proposed to determine the combined bearing and shear-out capacity. The proposed equation is demonstrated through verification against independent laboratory test results involving 5-mm plates of three different grades to be significantly more accurate than the simple sum. Explanation for the unexplained results obtained by another researcher using his own equation is provided in this paper.

The research presented in this paper examines the shear resistance performance of self-tapping screws (STS) in three-ply cross-laminated timber (CLT) panels. Specifically, the feasibility of using innovative STS assemblies with double inclination of fasteners was investigated for the shear connection of CLT panels. The specimens ($1.5\times 1.5\mathrm{m}$) were subjected to quasi-static and reversed-cyclic loading. The tests were set up to approximate pure shear loading, with three-panel CLT assemblies connected with STS. The resulting load-displacement and hysteretic curves were used to determine an equivalent energy elastic-plastic curve to estimate assembly capacity, yield load, yield displacement, ductility ratio, stiffness, and damping. Excellent structural performance in terms of capacity and stiffness was obtained while still providing the required ductility for the system to be used in seismic applications. The average static and cyclic yield loads were $6.0\mathrm{kN}/\mathrm{screw}$ and $5.9\mathrm{kN}/\mathrm{screw}$, respectively. Average static and cyclic and ductility ratios were 7.7 and 4.1, respectively, allowing the connection to be classified as highly ductile under quasi-static loading and moderately ductile under reversed cyclic loading. The data obtained allow engineers to specify an innovative connection assembly with double inclination of fasteners for lateral load–resisting systems of CLT structures.

Old structures are frequently modified to comply with current living standards and/or legislation. Such modifications may include the addition of new windows or doors and paths for ventilation and heating systems, all of which require openings to be cut into structural walls. However, effects of the required openings are not sufficiently understood. Thus, the objective of the work reported here was to analyze openings’ effects on the axial strength of large concrete wall panels. Three half-scaled walls with two opening configurations, corresponding to small and large door openings, were subjected to a uniformly distributed axial load with a small eccentricity. The results indicate that the 25 and 50% reductions in cross-sectional area of the solid wall caused by introducing the small and large openings reduced the load-carrying capacity by nearly 36 and 50%, respectively. The failure progression was captured using digital image correlation technique and the results indicated involvement of a plate mechanism rather than uniaxial behavior as adopted in current design codes. Using a simplified procedure, the load-carrying capacity was predicted using existing design models found in the research literature and design codes.

To accurately identify the nonlinear damping ratio of tall buildings, the authors propose an envelope random decrement technique (RDT). To verify the accuracy of the envelope RDT for the evaluation of amplitude-dependent nonlinear damping ratio, an iterative computing method, which can accurately work out the response of structures whose parameters depend on the response amplitude in any form, is also proposed. Then, using three different damping models in the numerical simulations, of which the response is calculated by the proposed iterative computing method, the applicabilities of traditional RDT, RDT ranked by peak amplitude, and the envelope RDT presented in this paper for the evaluation of amplitude-dependent nonlinear damping ratio are analyzed and compared. Results indicate that envelope RDT is better than the other two methods for the evaluation of amplitude-dependent nonlinear damping ratio. Finally, the envelope RDT is applied to identify the damping ratios of the Shanghai World Financial Center.

Widespread damage to welded unreinforced flange-bolted web (WUF-B) steel moment connections during the 1994 Northridge earthquake led to intensive research study of this connection. Despite the improvements to weld metal and connection details, the post-Northridge WUF-B connection was unable to attain sufficient ductility for use in special moment frames (SMFs). This study presents detailed finite element (FE) analysis of post-Northridge WUF-B connections to better understand the mechanisms which limited connection ductility in laboratory tests. Observations made from the FE analysis led to the development and numerical study of a modified WUF-B connection that combines a new bolted web design with a recently validated technique to promote plastic hinging of the beam away from the connection joint. The proposed connection provides the benefit of reduced field welding and UT inspection without sacrificing connection ductility and seismic performance. Finally, the proposed connection is experimentally validated through full-scale seismic testing. The pilot test specimen exceeded the AISC 341 qualifying 4% interstory drift angle without significant strength loss. No weld or near-weld cracks were observed. Instead, failure of the connection resulted from large local buckling deformation in the plastic hinge away from the welded joint.

This paper discusses a research program aimed at defining accurate limit-state displacements that relate to specific levels of damage in reinforced concrete bridge columns subjected to seismic hazards. In design, concrete compressive and steel tensile strain limits are related to column deformations through the use of an equivalent curvature distribution. An experimental study was carried out to assess the performance of 30 circular well-confined bridge columns. Material strains, cross-section curvatures, and fixed-end rotations attributed to strain penetration of reinforcement into the adjoining member were quantified by using a three-dimesional (3D) position monitoring system. An equivalent curvature distribution was created that reflects the measured spread of plasticity and components of deformation. When compared with the current approach, the proposed modified plastic-hinge method improved the accuracy of both tensile and compressive strain-displacement predictions, while maintaining similar levels of accuracy for elastic displacements. These recommendations, combined with material strain limits defined in the larger research program, serve as input into a displacement-based design procedure to achieve a defined level of performance under a specific seismic hazard.

A simple procedure to calibrate the safety factor of capacity models is presented. The calibration can be carried out based on any available database of experimental tests, even of limited size. The procedure aims to assess the model capability of predicting the test results and to calibrate the safety factor so that the capacity equation meets the target reliability level required by the code or sought by the calibrator. After predicting each test of the database with the capacity equation under consideration, the test-prediction pairs are checked for the property of linearity, and the relative error for the properties of homoscedasticity and normality. Once these properties are fulfilled—which may require a nonlinear transformation of the test values and/or the predictions—the closed-form equation proposed in this paper is employed to compute a target design value. The model safety factor is finally obtained by comparing such target design value with the design value obtained from the code. The paper also proposes two approximate analytical equations to compute the tolerance factor, used to attain any given fractile, as a function of the (even small) number of tests, with any assigned confidence level. A fundamental outcome of the procedure is that it yields an objective indicator of the model accuracy, measured by the standard deviation of its error, which may be regarded as a parameter useful for selecting the most reliable model among different competing ones. In the long run, the application of the proposed procedure will allow achieving a uniform reliability level throughout all capacity models used in codes and guidelines. A further advantage is that the partial safety factors so derived can be straightforwardly updated when more experiments become available. As an example, the proposed procedure is herein applied to the ACI 318 shear design capacity equation for concrete members unreinforced in shear.

Design and analysis procedures for buildings with fluidic self-centering systems are presented and evaluated. The design procedures parallel those for buildings with damping systems in Chapter 18 of the ASCE 7 Standard. The evaluation of the procedures is based on the design and nonlinear response history analysis of 3- and 6- story steel moment frame example buildings. The study establishes the validity of simplified methods of analysis and determines their range of accuracy. Specifically, the simplified methods of analysis provide good and most often conservative estimates of drift and good predictions of self-centering device forces. The results demonstrated that buildings equipped with fluidic self-centering devices and designed per the presented procedures offer benefits of substantial reduction in residual story drift but also reduced peak story drift, peak floor acceleration, peak story shear and base shear forces, and reduced floor acceleration response spectra by comparison to the code-complaint moment resisting framed buildings without fluidic self-centering devices.

The lack of a standard accepted method to estimate local peak pressure coefficients from wind tunnel data can lead to inconsistent definitions and interpretations, particularly because cost and time constraints associated with wind tunnel tests of low-rise buildings necessitate relatively short (equivalent full-scale) durations. This paper focuses on a Gumbel distribution fitting method widely used in practice. Because the sources of uncertainty regarding estimated peaks include the use of short-duration records (in practice) and the assumption that the observed peaks from wind tunnel pressure data are Gumbel-distributed, this is quantified in detail in terms of the parameters determining the required minimum record length. It is shown that 15 observed peaks can lead to local peak pressure estimates with adequate precision for many design scenarios. However, the conversion of peak coefficients from a short duration to those of a longer duration requires an increase in the number of observed peaks to maintain precision.

The fictitious force method (FFM) is an iterative nonlinear elastic analysis method of skeletal structures. The FFM extends the geometrically nonlinear $P\text{-}\mathrm{\Delta }$ method to the materially nonlinear analysis by replacing the original problem with an auxiliary linear problem that includes additional loads that account for the materially nonlinear behavior. The FFM is easily implemented in current linear finite-element analysis (FEA) programs. The FFM is mathematically equivalent to the modified Newton-Raphson method, which means that it converges linearly. The paper (1) applies a combination of FFM with a layers model (FFM-LM) to the quasistatic nonlinear analysis of reinforced concrete plane frames displaying bending-stretching coupling, (2) shows how to implement FFM-LM in a standard FEA program, and (3) applies the latter implementation to illustrative examples.

Using boundary elements in reinforced masonry (RM) walls allows closed ties to be used and multiple layers of vertical bars to be accommodated, thus providing a confining reinforcement cage. This enhances the overall performance of the RM wall with boundary elements relative to traditional RM walls with rectangular cross sections. This is attributed to the fact that traditional RM walls can typically only accommodate single-leg horizontal reinforcement and a single layer of vertical reinforcement because of practical limitations associated with concrete masonry unit geometrical configuration and construction techniques. Following the FEMA P695 methodology, “Quantification of Building Seismic Performance Factors,” the National Institute of Standards and Technology reported that some low-rise traditional rectangular RM walls (without boundary elements) might experience an excessive risk of collapse under the maximum considered earthquake (MCE). Moreover, although North American codes give seismic modification factors for RM shear walls with rectangular cross sections, no distinctive corresponding values are provided for RM shear walls with boundary elements. To address these issues, this study examines the effect of adopting the seismic response modification factors assigned for traditional RM shear walls on the collapse risk of RM shear walls with boundary elements. In this respect, OpenSees was used to create macro models to simulate the seismic response of 20 RM shear walls with boundary elements, designed with different configurations under different gravity load levels. The modeling approach was experimentally validated and the models were subsequently used to perform nonlinear static pushover analyses and incremental dynamic analyses following the FEMA P695 methodology. The analyses focused on evaluating the wall overstrength, period-based ductility, and seismic collapse margin ratios under the MCE. The results show that RM walls with boundary elements designed considering the ASCE7-10 force reduction factor currently assigned to RM walls with rectangular cross sections experience an enhanced performance that is enough to meet the FEMA P695 acceptance criteria for the expected seismic collapse risk under the MCE.

This paper introduces simple glued laminated (glulam) timber columns reinforced by near-surface-mounted carbon-fiber-reinforced polymer (CFRP) laminates (GTMC columns). Twenty-four columns were fabricated and tested under eccentric compression loading to validate the effectiveness of this kind of column. In accordance with the degrees of eccentricity, specimens were divided into three groups. In each group, one column without inlaid CFRP laminates served as a control column, while the others were inlaid with CFRP laminates. All columns were tested for ultimate load capacity, displacement ductility, failure mode, and energy dissipation capacity. Test results show that inlaid CFRP laminates are effective in increasing ultimate load capacity and deformability. Meanwhile, the corresponding analytical model was also derived to predict the ultimate load capacity of GTMC columns. A comparison of the predicted and tested ultimate load capacities demonstrated that the analytical model is generally able to evaluate the ultimate load capacity of GTMC columns with an average underestimation of 8.7%. Furthermore, a finite-element analysis was conducted to investigate the effects of thickness and mounted depth of CFRP laminates on ultimate load capacity and initial stiffness.

The seismic interaction of unanchored objects with a seismically qualified system or component in a nuclear power plant (NPP) can be detrimental to nuclear safety. In order to assess the seismic risk, an accurate quantification of the seismic response of unanchored components, such as spent-fuel dry storage casks, portable standby generators, electrical transformers, unreinforced masonry radiation shielding walls, etc., is required. The rocking response and toppling vulnerability of unanchored objects is not covered in nuclear standards, guidelines, and reports, except for an approximate method provided in ASCE/SEI 43-05 to estimate the maximum rocking angle in lieu of nonlinear time history analysis. In this study, the approximate method adopted by ASCE/SEI 43-05 is evaluated, first qualitatively and subsequently by comparing its predictions against results from a series of nonlinear time history analyses (NLTHA). The study concludes that the ASCE/SEI 43-05 method (which has also been adopted in FEMA P-58-1 and is expected to be adopted in the new revision of ASCE 4) provides highly unreliable, and in many cases unconservative, estimates of peak rocking rotation for a wide range of block geometries, under various levels of excitation. Because a reliable simplified method for estimating rocking rotations is not currently available, the paper recommends that rotation demands be obtained from nonlinear dynamic analysis.

Reinforced concrete members with significant geometric discontinuities or $D$-regions experience complex stress fields under loading, which require considerable analytical effort and usually complicated reinforcement detailing. Large openings in RC members can interrupt the direct load transfer provided by concrete struts, thereby leading to overstressed localized regions and unexpected failure modes. Empirically based strut-and-tie models (STMs) are generally used to design the reinforcement detailing of these RC members. However, many prior studies indicate that the resulting details can be very complicated while the actual stress fields deviate significantly from that assumed by STMs, thereby leading to unpredictable failure modes. This study investigates the feasibility of using steel fibers to replace the majority of conventional reinforcing bars in RC deep beams with significant $D$-regions. The test beams have two large openings, which are located between the loading point and the supports, thus disrupting the direct flow of forces. A simplified procedure is proposed for designing and detailing the reinforcement of steel fiber–reinforced concrete (SFRC) specimens based on the stress fields from elastic finite-element analyses. Experimental results show that when the critical regions of a test specimen were reinforced appropriately by conventional reinforcing bars and the remaining portion of that specimen was reinforced by SFRC with 1.0% volume fraction of fibers, the reinforced SFRC specimen exhibited a ductile failure mechanism with very large plastic deformation. The reinforced SFRC specimens also showed much higher strength than the nominal design load and experienced slow postpeak strength loss. In comparison, although the RC specimen reached very high strength, it also showed an unexpected brittleness and localized failure behavior. This study also shows that finite-element simulation based on the modified compression field theory (MCFT) is able to identify possible failure mechanisms of reinforced SFRC specimens.

Spatial variability of material properties might significantly affect the structural performance and reliability of unreinforced masonry (URM) walls. The paper develops a computational method to predict the strength for URM walls subject to one-way horizontal bending considering unit-to-unit spatial variability of the material properties of mortar joints and bricks. In this context, the term unit is being used to describe the location in the wall associated with a single brick and the adjacent mortar joints. In this way, the material properties are assumed to be uniform along the length, height, and thickness of individual bricks but may vary from brick to brick within the wall. Tensile strength, shear bond strength, and associated fracture energies of the mortar joints and tensile strength and fracture energy of the bricks are the main parameters considered herein. The authors examine how correlation and spatial variability in unit strengths (mortar joints and bricks) affect the variability of ultimate strength and damage progression of clay brick URM walls in one-way horizontal bending. Stochastic analysis in the form of Monte Carlo simulations used a three-dimensional (3D) nonlinear finite-element analysis. The results were validated from a database of available experimental results on masonry four-course beams. It was found that good agreement of peak load exists between the stochastic simulation and the experimental results for the four-course beam subject to horizontal bending.

A concrete strength-sensitive finite element (FE) model applicable to concrete subjected to various confining pressure levels and conditions is presented. This paper focuses primarily on the failure surface and flow rule of concrete in multiaxial compression, which were experimentally observed to vary with the unconfined concrete strength and level of confining pressure. To this end, a large experimental database, which consists of more than 1,700 results of concrete specimens tested under biaxial and triaxial compression, was assembled through an extensive review of the literature. This database was augmented with another test database of concrete in uniaxial compression that consists of more than 4,000 test results. Based on the test database results, it was observed that the tangential slope of the failure surface reduces with an increase in the unconfined concrete strength and confining pressure. The concrete dilation angle considered in the flow rule was observed to be nonlinear throughout loading history. To incorporate the observed changes in the failure surface and flow rule of concrete subjected to uniaxial, biaxial and triaxial compression, an extension of Lubliner’s concrete-damage plasticity model was proposed and presented in this paper. Comparisons with experimental test results show that the predictions of the extended model are in good agreement with the test results of both normal-strength concrete (NSC) and high-strength concrete (HSC).

This paper presents an experimental investigation to determine the embedment length required for longitudinal reinforcement in a bridge column extending into an oversized pile shaft, and the amount of transverse reinforcement required for the pile shaft to prevent premature bar anchorage failure due to concrete splitting induced by bar slip. Four full-scale column–oversized pile assemblies were tested under quasi-static cyclic lateral loading. The test specimens had different embedment lengths for the column reinforcement, different amounts of transverse reinforcement in the piles, different sizes of longitudinal bars, ranging from No. 8 to No. 18 (25 to 57 mm) bars, and different column-to-pile diameter ratios. All column–pile assemblies behaved in a ductile manner with plastic deformation occurring near the base of the columns despite some cone-shaped fractures and tensile splitting cracks occurring in the top portion of the piles. The test results show that the embedment length for the column reinforcement can be significantly reduced as compared to that required in current design specifications. The study also shows that an engineered steel casing designed according to a formula proposed here can effectively confine the pile shaft and significantly reduce splitting cracks.

A seismic design strategy, which is intended to be implemented within the framework of the U.S. seismic design provisions for steel structures, is presented for single-story steel concentrically braced frames that are divided into two tiers. In this method, the columns are designed to resist the axial loads acting in combination with the in-plane flexural demand resulting from uneven distribution of brace inelastic deformations over the frame height. This design procedure, which establishes enhanced requirements beyond the 2010 edition of the U.S. seismic design provisions, prevents concentration of deformation in one tier and causes frame nonlinear deformation to be distributed between the tiers. The column bending moments depend on the story shear resistance that develops in each tier when the bracing members are at buckling and in the postbuckling range. The method also aims to control tier drifts to protect the bracing members from excessive inelastic demand, which could cause brace fracture. Nonlinear static and dynamic analyses are performed to validate the proposed design procedure.

A closed-form solution to the effect of member deformations ($\delta$) on the inelastic response of RC bridge columns is presented. The formulation is based on an equivalent elastic structure with a constant flexural stiffness for the cracked RC section that enables the solution to be independent of the structural global displacements ($\mathrm{\Delta }$). The ability of the proposed solution for predicting moment, curvature, and displacement profiles in RC columns is demonstrated and verified against experimental data from four half-scale test columns. The closed-form solution led to the identification of a dimensionless slenderness parameter that measures the susceptibility of RC columns to second-order effects. Simplified formulas for the spread of the plastic region ($L_{pr}$) and the magnitude of $P\text{-}\delta$ moment are proposed for use in seismic design. The design formulas, derived from the mechanics-based solution, are shown to be able to predict experimental data on the $P\text{-}\delta$ effects with satisfactory accuracy.

The design of structural concrete using strut-tie models requires establishing the effective strength of concrete struts, ensuring sufficient anchorage of reinforcing bars in nodal zones, and the geometric compatibility of the strut-tie model within the member geometry. In this paper, a consistent and general method applicable to three-dimensional (3D) strut-tie models is presented. The proposed method includes the effects of 3D stresses associated with tensile strains in reinforcing bars crossing a strut, strut length, deviation angle between strut orientation and compressive principal stress flow, compressive strength of concrete, and degree of confinement provided by reinforcement. The proposed method is implemented and then verified using data from 115 reinforced concrete pile caps tested to failure.

Membrane fabric structures are spatial structures that allow for long span and lightweight roofs. In many cases, membrane roofs are supported with trusses or masts and prestressed together with cables to obtain a resistant shape for a given loading condition. For the design of membrane structures, geometrically nonlinear analysis is required. Additionally, modeling of each membrane element and form-finding of the shape are of great importance in the design process. First, an equilibrium-finding analysis is conducted for the purpose of obtaining the optimal shape of the membrane structure, during which the initial stresses of the membrane and cables must be balanced. Next, the stress-deformation analysis is performed for the required loading condition. This analysis allows understanding of the behavior of the structure and confirms that the design of the membrane satisfies the required safety factor for the construction. The analyses of the Southwestern Baseball Dome in Seoul and the Jeju Stadium Dome in Jeju Island, both in Korea, are presented, with an emphasis on details in all aspects of the analysis process. It is found that the selection of analysis and design techniques and appropriate construction materials would be most critical. The analysis results also show that the form-finding step has a significant effect on increasing the stiffness of the structure and a more regular geometry promotes a more stable response under various loading conditions.