Journal of Structural Engineering

Substantial attention has been paid to precast structures due to their obvious advantages. While precast members connected by grouted sleeves are used in seismic regions, studies on the seismic performance of precast column under large axial compression ratio are few, especially in underground structures. In this paper, three full-scale precast columns were designed and tested under axial compression ratios of 0.2, 0.5, and 0.85. Additionally, three monolithic cast-in-place columns with identical details served as a control. The main objectives of this study are to study the influence of the axial compression ratio on the global mechanical behavior of precast columns subjected to low-cyclic reversed horizontal loads, and to discover the internal force distribution and reach the appropriate axial compression ratio for precast columns. The test results are: (1) Precast columns were capable of matching the deformation and lateral strength of monolithic connections under the same compression ratio, while they were affected significantly by the axial compression ratio. (2) The plastic hinge location of precast columns shifted above the grouted sleeve region. It is found that good ductility can be exhibited compared with conventional cast-in-place column. (3) An effective measure to relieve uncoordinated stiffness along the height of the column was introduced. (4) Based on strength and deformation with the same axial compression ratio, the appropriate axial compression ratio was achieved for precast columns and the relationship of spliced-bar strain ratio and axial compression ratio was presented.

Strut-and-tie modeling (STM) has been proven to conservatively predict the strength of specialty concrete structures such as corbels, dapped ends, and deep beams with openings. The objectives of this study were to predict the strength of masonry beams with openings using STM and evaluate the effect of transverse reinforcement in masonry beams. To this end, a suite of 23 tests was conducted on masonry beams with openings of various sizes and locations. When experimental data are compared to various strut-and-tie models, results confirm that STM provides conservative predictions for the strengths of masonry beams with openings. Furthermore, beams with transverse reinforcement at the openings did not perform significantly better than beams without transversely reinforced openings.

Strongback-braced frames employ an essentially elastic truss, or strongback, that defines an elastic load path to redistribute seismic demands and mitigate the formation of story mechanisms. However, unlike the forces from traditional capacity design—which assumes that inelastic response limits the earthquake-induced forces—design forces in the strongback arise from a nonlinear first mode and near-elastic higher-mode response, because the strongback is designed to remain elastic in every mode. A design method using modal pushover analysis, which combines the response from pushover analyses in multiple modes, can estimate the magnitude and distribution of the force demands in the first and higher modes, including inelastic response. The existing modal pushover analysis procedure is simplified and applied to the design of the strongback in strongback-braced frames. Accounting for only the first mode of response resulted in estimates below the 16th percentile of force demands extracted from nonlinear dynamic analysis. However, a modal pushover approach using multiple modes resulted in improved estimates able to represent both the distribution and magnitude of the peak force demands from nonlinear dynamic analysis of eight- and four-story strongback-braced frames with buckling-restrained braces, while maintaining the conceptual simplicity of nonlinear static analysis procedures.

In the present experimental study, 12 specimens were tested to assess and quantify the effects of bolt tightness on the overall behavior of a bolt-ball joint under uniaxial loading. A three-dimensional (3D) nonlinear finite-element (NFE) model with all geometrical complexities, including the threads, was developed to examine the significance of bolt tightness on overall behavior. Three types of parameters were studied, namely, tightness torque, material properties, and friction coefficients. The tests showed that the tightness torque moments had a significant effect on the axial stiffness of the specimens under compressive loading. Observations during the tests indicated that the bolt and sleeve had important roles in the load transferring mechanism. Based on the results of the current experimental study, the finite-element model (FEM) was verified against the test specimens. An acceptable qualitative agreement was observed between the FE models and the experiments for the axial behavior of the joint. It was found that the material properties had a significant role in changing the failure mode and load-bearing capacity. Based on experimental tests and NFE analyses, the present study provides a nonlinear model for determining the relationship between the torque and the preload using gene expression programming. It was concluded that the simplified formulation proposed in this study can calculate the relationship between the torque and the initial load against the bolt tightness database with good accuracy.

This study investigated the behavior of end-plate connections for column splices with construction tolerance. To adjust misalignment between upper and lower columns, oversize holes were drilled on the end plate and plate washers were then placed to bridge over the oversize holes under the head or nut. Six columns with the misaligned connection in the plastic hinge region were tested under cyclic loads. Test variables considered were misalignments, end-plate details (i.e., thickness and stiffener), and the flexural capacity of columns. The test results showed that although plastic deformations occurred significantly near the connection with misalignment, the connection performance of the columns was good: prying action and plate deformation at the connection were minimized although the connection strength of the end plate was only 60% of the required strength because the plate washers provided additional resistance. In addition, slip deformation on the faying surface was negligible due to the preloads of fully tightened bolts. The stiffened end plate was effective in reducing the required thickness of end plate, whereas the shim plate between the top and bottom end plates slightly degraded the slip resistance. The force-transfer mechanism at the end-plate connection under axial compression was investigated and verified through finite-element analysis.

Using residual displacement as a measurable indicator can reduce subjectivity and uncertainties in postearthquake assessments. However, the accuracy of analytical models in predicting displacements, particularly residual displacement, has always been an obstacle in this field. This paper aims to fill the gap in the literature on a proper method to enhance the analytical predictions. A comprehensive parametric investigation on the accuracy of distributed plasticity models was carried out, with a focus on bridges under near-field motions. These parameters include influential nonlinear modeling parameters, loading history, viscous damping, and strain rate. The results of the 20 considered models are compared with the six available shake table test results, and two methods are proposed to enhance the displacement predictions for practical cases. In the first method, actual maximum and residual displacements can be determined with the desired confidence level. In the second method, nonlinear regression analysis based on many influential parameters is conducted to enhance the accuracy of analytical residual displacement. This method considerably reduces the model error compared to the available methods in the literature.

A new analysis approach is devised herein to predict the response of reinforced concrete deep beams strengthened in flexure, shear or shear-flexure with fiber-reinforced polymer (FRP). The analysis approach recognizes the fact that FRP-strengthened deep beams represent a statically indeterminate idealized truss. Therefore, two parallel determinate trusses are modeled for the levels of yielding and ultimate loads. By imposing the compatibility of deflections between the two trusses at the yielding and ultimate levels, the contribution of the second truss is evaluated using the load obtained from the first truss. The nonlinear strain profile is adjusted to account for the Timoshenko first-order shear deformation contribution. The analysis procedure is examined against four different deep beams strengthened in flexure, shear, and combined shear-flexure and tested experimentally. The predicted full response agrees very well with all experimental curves. In addition, the analytical and experimental responses of five extra-deep beams are compared for added verification. Accordingly, this approach may be viewed as a unified procedure to analyze the whole spectrum of strengthened deep beams.

Millions of people still live in cave dwellings in China and around the world. Due to high risk of earthquakes combined with material deterioration, cave dwellings exhibit poor seismic performance. Accordingly, a low-cost and highly efficient repair technique for damaged brick cave dwellings is needed. This paper presents shake table testing results for seismically damaged 1:4-scale brick cave dwelling models repaired using a cement mortar coating with polypropylene packing strap mesh. The seismic response of the repaired cave dwellings is presented in terms of damping ratio, acceleration, interstory drift, torsion angle, base shear, and hysteretic energy dissipation. Full peeling off between the cave sidewalls and the back wall as well as the plastic hinge at the bottom of the sidewalls led to the failure of the repaired cave dwellings. The damping ratios of the repaired cave dwelling models in the $x$- and $y$-directions were 2.23 and 2.74 times that of the initial values, respectively. The maximum story drift and horizontal torsion angle of the models at peak ground acceleration $(\mathrm{PGA})=1.00\mathrm{g}$ were 1/29 and 0.0015 rad, respectively. The use of a cement mortar coating with polypropylene (PP) packing strap mesh to repair the brick cave structure resulted in acceptable seismic performance.

The present paper reports in-depth experimental and numerical studies of the cross-sectional behavior and resistances of austenitic stainless steel welded I-sections under combined compression and major-axis bending moment. A testing program was first performed, which employed two austenitic stainless steel welded I-sections and included initial local geometric imperfection measurements and 10 major-axis eccentric compression tests. Following the testing program, a numerical modeling program was conducted, where finite-element models were developed and validated against the test results and then employed to conduct parametric studies to generate further numerical data over a wide range of cross-section dimensions and loading combinations. On the basis of the obtained test and numerical data, the accuracy of the design interaction curves given in the European code and American design guide for austenitic stainless steel welded I-sections under major-axis combined loading was evaluated. The evaluation results generally indicated that the codified design interaction curves yield excessively conservative cross-section resistance predictions, mainly due to the conservative end points, as determined without considering material strain hardening. Finally, new design interaction curves were proposed through adopting the European code design interaction curves anchored to more accurate end points, as calculated with rational exploitation of material strain hardening by the continuous strength method. The new design interaction curves were found to offer significantly improved design accuracy than their codified counterparts. The reliability of the new design interaction curves was confirmed by means of statistical analyses.

A finite-element formulation is presented for the elastic distortional buckling analysis of doubly symmetric wide flange beams. The formulation characterizes the distribution of the lateral displacement along the web height through Fourier modes and is equipped with features to capture the load height effect and to enforce user-defined kinematic constraints. The formulation is used to investigate the load height and bracing height effects and develop a database of over 20,000 runs on practical beam cross-sections to characterize (1) the reduction in critical moment capacity due to web distortion; and (2) the effect of a load height on the elastic critical moments. A novel indicator characterizing web distortion along the beam span is proposed and integrated within the finite-element formulation in a procedure devised to optimize the location of transverse stiffener(s) along beam spans so as to reduce cross-sectional distortion and maximize the elastic critical moment attainable. The procedure is then applied to optimize the design of beams in two case studies.

In this study, a model is proposed to determine the required lap-splice length in RC beams using a multilayer genetic programming machine learning (MLGPML) algorithm. This model was obtained from the study of the bond stress between concrete with normal and high compressive strength and tensile reinforcement. Previous models were used to estimate this bond stress, taking into account different parameters. In this study, using the results of 386 experimental tests on reinforced concrete beams, the lap-splice length and the required transverse reinforcement over that length were calculated. The proposed model to determine the bond stress is very well suited to the design purposes by comparison with various experimental campaigns’ results.

As a kind of typical air-inflated membrane structure, ethylene–tetrafluoroethylene (ETFE) cushion has become one of the most essential engineering structures in recent decades, especially in the field of large-span spatial structures. This study experimentally investigates the mechanical properties and structural behaviors of ETFE cushion structures subjected to progressive wind loading. Specifically, two identical ETFE cushion models were fabricated based on a three-dimensional patterning design for assembling the experimental system. Progressive wind loading was efficiently simulated by applying air pressure difference directly on the membrane surface by adjusting the internal pressure of an airtight load simulation chamber that was directly connected to the ETFE cushion. The complete experimental system of each ETFE cushion model was acquired by integrating an automatic pressure control device and a measurement device. The ultimate bearing capacities of the structure models were evaluated separately through destructive tests under the progressive wind pressure and suction loads. The internal pressures, geometric shapes, strain distributions, stress distributions, and failure modes of the two ETFE cushion models were monitored and analyzed. In the wind pressure test, the ETFE cushion model was destroyed owing to the tearing destruction of edges under the ultimate bearing capacity of 20 kPa and the maximum membrane stress of 49.8 MPa. In the wind suction test, the ultimate bearing capacity and maximum stress of the structure model were $-10\mathrm{kPa}$ and 40.6 MPa respectively with the tearing breaks on the central welding seams and edges. These insights and findings inspired by the experimental investigations are significant for the structural analysis, optimal design, and safety evaluation of ETFE cushion structures.

The beam–column element analysis method has been extensively adopted in practice, relying on the robustness of its element formulation. Steel members with open sections are commonly used; their cross-sectional shapes are usually nonsymmetric to improve material efficiency. Nevertheless, an offset exists between the shear center and the centroid of a nonsymmetric section. If the applied loads do not act at the shear center, torsion can be induced; this is sometimes unavoidable. When a member is subject to torsion, the inclined angle between the local axes of the cross section and the element is varied along the element length, complicating the summating of the cross section’s stiffness to form an element stiffness matrix. This study developed a new beam–column element formulation based on the nonsymmetric section assumption and a Gaussian quadrature procedure to formulate the element stiffness matrix of being concise in expressing formulation. The updated Lagrangian method was modified to consider large deflections. This method permitted the use of fewer elements to simulate a member under torsion, leading to a significant improvement in numerical efficiency. Detailed derivations and verification examples are given in the paper.

Brittle failure of lightly reinforced concrete columns is one of the primary reasons for partial or total collapse of substandard existing buildings subjected to earthquake loading. This study presents collapse performance of a full-scale building that was performed to gain insight into the seismic behavior and the collapse mechanisms of nonductile buildings with lightly reinforced concrete columns. The three-story building was tested under displacement-controlled quasi-static reversed cyclic loading followed by a lateral pushover loading up to realization of the total collapse. In addition to the poor reinforcement details, columns had high axial load–to–axial capacity ratios as also observed in many existing substandard buildings. During the test, severe structural damage was observed at 0.9% first-story drift ratio in the cyclic part of the lateral loading and the brittle total collapse of the building took place during the pushover loading at 1.45% first-story drift ratio. In this paper, after the introduction of the test campaign, the formation of structural damage and collapse mechanisms are discussed. In addition, an attempt to predict the behavior and performance of the test building is made by using a column model that considers flexural, slip, and shear deformations. Finally, the obtained analytical results are compared with the experimental observations and results.

This paper presents experimental and numerical investigations on the flexural behavior of reinforced concrete beams strengthened with near-surface mounted high-strength aluminum alloy (AA) bars subjected to four-point bending load. A total of five RC beams, including one control beam and four beams strengthened using near-surface mounted (NSM) AA bars with or without CFRP U-warp end anchorage, were constructed and tested monotonically up to failure. To get a better understanding of the flexural behavior and failure mechanism of the tested specimens, 3D finite element models were developed. A comparison between the finite element (FE) and experimental results was carried out and therefore confirmed the ability of the developed FE models to accurately predict the flexural performance of the RC beams strengthened with NSM AA bars. In addition, FE simulations provided an in-depth investigation of the intermediate crack-induced debonding (ICD) and concrete cover separation (CCS) failures. It is observed from the experimental and FE results that compared to the control specimen, more than 34% increase in the load-carrying capacity of the NSM strengthened specimens was achieved. In addition, the CFRP U-wrap end anchorage contributed to the prevention or delay of the CCS and ICD failures and hence increased the load-carrying capacity and enhanced the displacement ductility of the strengthened beam specimens. Furthermore, a FE parametric study was carried out to investigate the influence of different parameters on the performance of the RC beams strengthened with NSM AA bars, and recommendations based on the parametric study for efficient application of the NSM strengthening technique were given.

A novel bolt-connected precast concrete wall panel structural system has recently been proposed for low-rise buildings in rural areas. The system features replaceable distributed bolt-connections adjoining walls, floors, and connecting columns fixed in base, enabling the whole system to be demountable and remountable. Previous quasi-static cyclic push-over test results showed an unfavorable punching shear failure of bolted joints without fully mobilizing the strength of the wall panels. Therefore, the connections were strengthened by using high-strength bolts and adjusting the positions of bolts. In order to evaluate the seismic performance of the precast system with the improved connections, incremental dynamic shake table tests were performed on a full-scale two-story building. Seismic demands and capacities of the precast building with connecting columns fixed in base (Model I) and without fixed-base constraints (Model II) were compared. The experimental results highlighted the high capacity of the improved precast system against beyond design-basis earthquakes with a peak ground acceleration of up to 0.8 g. Only slight to moderate damage was observed in terms of cracks at the edges of the door/window openings, similar to those on a cast-in-place structure, followed by cracks on concrete at connections. Although Model I showed higher lateral stiffness and lower seismic fragility, seismic energy was dissipated more evenly throughout the whole structure of Model II, which was proven well suited for low-rise buildings. Insight was given to explain the improvements on the bolt connections and the reinforcing effects of the connecting columns to provide references for the potential application of the proposed precast system.

This paper presents the experimental results of an innovative configuration for cold-formed steel (CFS) framed shear walls using corrugated steel sheets as sheathing material. The shear wall configuration comprises corrugated steel sheathings placed inside the steel framing and therefore is known as an in-frame or sheet-in shear wall. The innovative shear wall configuration is noncombustible, is equal in thickness to adjacent walls, and avoids the difficulties inherent in the design and installation of the finish materials used in common corrugated steel sheathed shear walls. The test program in this research comprised cyclic testing of five groups of shear walls in which the stud arrangement, sheathing continuity, framing thickness, and wall aspect ratio varied. The results indicate that shear walls with a lower-profiled field stud and continuous sheathing had satisfactory performance with balanced shear strength and ease of assembly. Based on the test data, shear resistances of in-frame or sheet-in shear walls with corrugated steel sheathing under seismic load are recommended as the basis for design. These innovative shear walls exhibited substantially higher shear capacity than code-certified shear walls, and therefore can be used as a substitute for a lateral force–resisting system in midrise CFS light-framed buildings.

This paper presents the results of a series of unidirectional quasi-static cyclic tests on 1/3-scale post-tensioned rocking steel bridge column specimens designed to rock at the interface with the foundation. The objective was to examine the effects of column diameter-to-thickness ratio, base plate, and energy dissipaters and their locations on the lateral cyclic behavior of the system. Site-specific cyclic displacement loading protocols were developed by performing time-history analyses of the pier. Emphasis was placed upon the sources of lateral response degradation including elastic restoring force reduction, local buckling, and energy dissipater failure. Strain distribution at the rocking plane and along the height, local bulging of the column, and uplift profile are discussed. The influence of multiple loading on the lateral response was also investigated. A component testing program was conducted to characterize the cyclic loss of post-tension force due to wedge seating in a typical industry monostrand anchorage system. The column test results demonstrate that a stable and robust self-centering response can be achieved with minimal damage to the column and most of the hysteretic energy is confined within the replaceable elements.

Fiber-optic sensing (FOS) provides distributed strain measurement that can enhance both structural health monitoring (SHM) and laboratory testing capabilities. In particular, optical frequency domain reflectometry (OFDR) provides strain or temperature measurements every millimeter over tens of meters of fiber, with a high sampling rate. For RC applications with embedded fiber-optic cables, the sensitivity of the fibers and their ability to measure and survive cracking are both important considerations. In this study, tests were conducted on six RC specimens to investigate the effectiveness of using OFDR strain sensing to evaluate the cracking behavior of concrete and the deformation of steel reinforcing bars. Six types of fiber-optic cables with very different structures, sensitivity, and survivability were tested. Fibers were placed in the concrete and in grooves in the reinforcing bars. A new deconvolution method was developed; using the method, crack widths were accurately measured up to the target load levels using both the more sensitive fiber-optic cables and cables with reduced sensitivity but better survivability. OFDR strain sensing, combined with new methods of data processing, was shown to be capable of detecting distributed microcracking and providing reliable crack widths. The OFDR technique was also used to reveal the location-dependent bond-slip relationships between the concrete and rebar at early stages.

Estimation of statistical moments remains one of the main topics of stochastic analysis whose accuracy greatly affects reliability analysis results. In this work, conjugate unscented transformation (CUT) methods, which can balance accuracy and efficiency, are introduced for the statistical moment estimation of responses. Because of the drawbacks of existing CUT methods, a family of enhanced conjugate unscented transformation (ECUT) methods, including ECUT-4, ECUT-6, and ECUT-8 methods, is proposed for statistical moment estimation by combining the original CUT, variable transformation, and exact dimension reduction method. Then the probability density function of a performance function is reconstructed by the improved maximum entropy method (IMEM) with the available statistical moments as constraints. To demonstrate the accuracy and effectiveness of the proposed methods, five numerical examples, including linear and nonlinear, low-dimensional and high-dimensional, and explicit and implicit performance functions, are investigated, in which the results obtained from the proposed methods are compared with other existing moment methods and a Monte Carlo simulation (MCS) method. The results of the examples show that the proposed ECUT-6 and ECUT-8 methods have fairly high accuracy and efficiency for structural reliability analysis.

A novel hybrid fiber-reinforced polymer (FRP)-aluminum space truss structure with pretightened teeth connections (PTTCs) and aluminum-bolt-ball connecting system (ABCS) that can be used as part of pedestrian bridges, platforms in marine areas, or roof structures is proposed. To understand the failure modes, bearing mechanism, and flexural behavior of the structure, three-point bending tests were conducted. Three loading scenarios were designed to investigate the impacts of different joint conditions. Each scenario presented different structural loading responses. Promoting the bolt stiffness and strength of ABCS improved the structural stiffness and ultimate load. The structural ductility was greatly increased by introducing joint ductility. A solid-element model of the ABCS simulated the joint loading behavior. The fine-line element structural model was established considering the joint stiffness extracted from the finite-element (FE) analysis of the ABCS model. Both models were validated by experiments.

Slender load-bearing masonry walls are typically used in low-rise commercial and industrial settings, where they are an efficient system to resist out-of-plane forces and gravity loads. Masonry walls are usually built upon concrete footings, with their first course mortared upon the concrete surface, and their reinforcement is spliced to dowels cast into the foundation. Despite the inherent rotational stiffness of this type of connection, when the walls are slender (height-to-thickness ratio $>30$) North American masonry codes direct the designer to assume a pinned condition at the base, neglecting the rotational stiffness provided by the foundation. This is because of the valid concern that the damage at the base under cyclic loading degrades the connection rapidly, turning it effectively into a hinge for structural purposes. Due to the scarcity of experimental studies on this topic, the objectives of this study are to (1) quantify the reactive rotational stiffness at the support for typical foundations used in masonry construction, (2) assess the increase in load-bearing capacity provided by the base stiffness during cyclic load, (3) investigate the base damage, and (4) determine the effect of the foundation stiffness on critical aspects of the structural response of the walls, such as stiffness, ultimate capacity, energy dissipation, and failure modes. To accomplish this, four moderately slender load-bearing masonry block walls were built with different degrees of base stiffness and tested under a combination of gravity and nonreversed cyclic lateral loads. Results from the tests showed an increase in load-bearing capacity and decreased deflections with increased rotational base stiffness. The walls achieved their ultimate loading capacity with little to no degradation at the base during the experiment. The moment capacity of the walls obtained during the tests exceeded that predicted by the design provisions. These results suggest that accounting for the additional strength provided by the base may be important for the design of other elements connected to the walls. It also highlights the need for additional cyclic testing on masonry walls with higher slenderness, accounting for the presence of a rotational stiffness at the base.

This paper presents a probabilistic framework for estimating the time-variant seismic fragility of high-rise buildings under carbonation-induced corrosion with a multiple damage model. A 42-story steel frame RC core tube (SFRCT) building was selected as a representative high-rise building to illustrate the proposed method. The main novelties of this study are that (1) a Bayesian updating method is used to determine the posterior probability distributions of the unknown parameters in the time-varying demand models of the maximum interstory drift and the residual drift at the top floor, (2) an analytical derivation method is used to compute the probability distribution of the corrosion initiation time in reinforcements, (3) the uncertainties associated with the corrosion initiation time and unknown parameters in demand models are incorporated into fragility estimates based on total probability theory, and (4) the elliptical copula and Archimedean copula are used to develop bivariate fragility estimates that consider the correlations among the limit states associated with maximum drifts and residual drifts, respectively. The results indicate that the seismic demand and fragility estimates of this high-rise building increase as the corrosion initiation time, which highlights the necessity of accounting for the uncertainty in the corrosion initiation time. In addition, the Gaussian copula and the Clayton copula (special cases of the elliptical copula and the Archimedean copula, respectively) produce similar joint probability distributions for the two-dimensional limit states; however, the Clayton copula can be used in a more general condition. The proposed methodology is applicable for evaluating the seismic life-cycle fragility of both existing and new high-rise buildings under multicriteria performance indicators.

This paper presents a new stochastic methodology for evaluating and quantifying the downtime of a structure in terms of a family of fragilities that represent the probability of exceeding prescribed times to return to functionality. This methodology integrates several existing concepts, namely, Federal Emergency Management Agency P-58 and Resilience-based Earthquake Design Initiative (REDi), to build a family of system (building) level fragility curves corresponding to the time needed to achieve different recovery levels (reoccupancy, functional recovery, and full recovery). This approach enables one to propagate uncertainty throughout the procedure so that variations in the delay time and repair schedules are accounted for in the resulting fragilities. As an illustrative example of this approach, the methodology is applied to assess the downtime of a two-story mass timber building that was originally tested at the NHERI@UCSD outdoor shake table in 2017. One unique aspect of this analysis is that it incorporates a relatively new material, cross-laminated timber (CLT), in a resilient posttension rocking wall design application. Nonstructural components representing a typical office building were selected and incorporated into the procedure for the two-story CLT rocking wall building. Time-to-functionality fragility curves are then developed for the two-story building, and potential design and resilience-focused applications are discussed.

Wire arc additive manufacturing (WAAM) is a method of metal three-dimensional (3D) printing that has the potential for a significant impact on the construction industry due to its ability to produce large parts with reasonable printing times and costs. However, there is currently a lack of fundamental data on the performance of structural elements produced using this method of manufacturing. Seeking to bridge this gap, the compressive behavior and resistance of WAAM square hollow sections (SHS) are investigated in this paper. In a previous study by the authors, testing reported of sheet material produced in the same manner as the studied SHS is first summarized. The production, measurement, and testing of a series of stainless steel SHS stub columns are then described. Regular cross-section profiles were chosen to isolate the influence of 3D printing and enable direct comparisons to be made against equivalent sections produced using traditional methods of manufacturing. A range of cross-section sizes and thicknesses were considered to achieve variations in the local cross-sectional slenderness of the tested specimens, allowing the influence of local buckling to be assessed. Repeat tests enabled the variability in response between specimens to be evaluated; a total of 14 SHS stub columns of seven different local slendernesses was tested, covering all cross-section classes of AISC 370 and Eurocode 3. Advanced noncontact measurement techniques were employed to determine the as-built geometric properties, while digital image correlation measurements were used to provide detailed insight into the deformation characteristics of the test specimens. Owing to the higher geometric variability of WAAM relative to conventional forming processes, the tested 3D printed stub columns were found to exhibit more variable capacities between repeat specimens than is generally displayed by stainless steel SHS. Comparisons of the stub column test results with existing structural design rules highlight the need to allow for the weakening effect of the geometric undulations that are inherent to the WAAM process in order to achieve safe-sided strength predictions.

Reinforced concrete (RC) bridge piers of highway viaducts are exposed to the vehicular impact hazard with impact location usually close to the ground (i.e., bottom of the pier), thus resulting in dominant shear damage. Different simplified approaches for the assessment of RC bridge pier performance under impact loads are generally based on equivalent static models. One crucial element for these approaches is the determination of the static shear performances and residual axial capacity. Because of limited experimental results available under these conditions, six half-scale rectangular RC columns with different volumetric reinforcement ratios and axial compressive loads were tested under near-ground lateral loads with monotonic static conditions. Test results indicate a clear major diagonal crack at the bottom of RC columns with an inclination angle of approximately 30° below the point of application of the lateral load, and it eventually slips along the crack surface under axial loads followed by failure (i.e., loss of residual axial capacity). The increase in the volumetric reinforcement ratio significantly improves the shear deformation capacity and shear crack resistance with a slight increase in the shear capacity. The increase in the axial load can also slightly increase the shear capacity of the columns but is accompanied by a reduction in shear deformation capacity. Additionally, prediction performances of three commonly used shear capacity models for the case of RC columns under near-ground lateral loads are investigated. Finally, based on the test results, an existing residual axial capacity model is modified to improve its prediction performance.

Seismic response records were retrieved from the monitored 21-story (53.26-m-tall) typical Puerto Rican reinforced-concrete shear-wall dominated El Castillo Building in Mayaguez, 50 km from the mainshock epicenter of the January 7, 2020, ${\mathrm{M}}_{\mathrm{w}}6.4$ offshore Indios, Puerto Rico earthquake. The shear-wall-to-floor areas of the building are 0.97 and 3.49 in the longitudinal and transverse directions, respectively, and have a slenderness ratio of 3.0 in the transverse direction. Basement and top-floor peak accelerations were 5% g and 12.8% g, respectively. Additionally, records from a nearby free-field station indicate a site period of 0.16 s. No visible damage was observed in the building after the earthquake. Spectral ratios and system identification allow identification of the transverse, longitudinal, and torsional fundamental periods as 0.97, 0.88, and 0.81 s, respectively, and are consistent with ASCE/SEI 7-16 (2017) formula. Damping percentages are 4.5%, 3.4%, and 2.2%, respectively. The maximum drift ratios are 0.20% and 0.12% in the longitudinal and transverse directions, well below the damage threshold for structural elements of $\sim 0.5\%$.

Since 1999, a long research program has been underway in France with the aim of better understanding the mechanical behavior of timber connections in fire situations. This work includes an experimental component, with the performance of numerous tests on timber connections subjected to an ISO fire, and a numerical component, aimed at better identifying the parameters influencing the fire resistance of connections. The final objective is to propose an analytical method for designing timber connections in fire situations that is easy to use by engineers and more precise and efficient than the current regulations, whose field of application is limited. In this study, a simple analytical method, based on the state of knowledge acquired over the last $20\mathrm{years}$ and the experimental data available in France and elsewhere, is proposed with the aim of improving the current regulations. The proposed method is explained, the experimental data used in its development are provided, and the results obtained from this method are discussed and commented.

Timber floors are prone to exhibit vibration levels, which can cause discomfort to the occupants. In the last $20\mathrm{years}$, ambient vibration tests have become very popular due to the many advantages they have over traditional forced vibration tests when dealing with civil engineering structures. Furthermore, sensitivity analyses and black-box” optimization algorithms can support the development of refined finite-element models that accurately predict the structures’ responses based on the experimental modal parameters. However, applications of these methods and techniques to timber structures are scarce compared with traditional materials. This paper presents and discusses the findings of an experimental testing campaign on a lightweight timber floor. At first, each component of the assembly was tested separately under different boundary conditions. Then, the authors evaluated the behavior of the whole floor assembly. In a second step, the authors carried out a covariance-based sensitivity analysis of finite element (FE) models representative of the tested structures by varying the different members’ mechanical properties. The results of the sensitivity analysis highlighted the most influential parameters and supported the comparison among diverse FE models. As expected, the longitudinal modulus of elasticity is the most critical parameter, although the results are very dependent on the boundary conditions. Then automatic modal updating algorithms tuned the numerical model to test results. As a concluding remark, the experimental and numerical results were compared with the outcomes of a simplified analytical approach for the floor’s first natural frequency estimate based on current European standards.

The Noor III solar tower of the Ouarzazate Solar Power Station in Morocco is a very slender structure sensitive to wind excitations. Hence, tuned mass dampers (TMDs) were employed to reduce its wind-induced response. Finite-element modeling and wind-tunnel test results were employed to design the parameters of the TMD system. Four $10\text{-}\mathrm{t}$ TMDs with eddy-current damping (EC-TMD) were selected for implementation (via a customized steel frame) at the top of the solar tower (i.e., inside the receiver). The effectiveness of the designed TMDs in controlling the tower was numerically studied under free vibration and forced vibration. Then, considering design and modeling errors and the possible need for on-site adjustments of EC-TMD parameters, pendulum-type EC-TMDs were fabricated. Dynamic properties of the tower were identified based on field measurements. With the installation and adjustment of the four designed EC-TMDs, the damping ratio of the Noor III solar tower was enhanced from 0.72% to 3.78%. Field measurements of tower vibrations under strong winds with/without participation of the EC-TMDs showed that significant mitigation of wind-induced response was effectively achieved by the TMDs with eddy-current damping. In addition, the on-site acceleration measured on the prototype tower was compared with the acceleration obtained for the scale model in a wind tunnel to highlight the significant Reynolds number effects on the prediction of the wind-induced response of the solar tower structure.