Journal of Structural Engineering

An experimental and numerical study on the octagonal high-strength steel tubular stub columns under combined compression and bending is presented in this paper. Octagonal high-strength steel tubular stub column specimens with different sizes were prepared. Experiments were performed on these specimens under concentric compression or eccentric compression, which induced various combinations of compression and bending on the structures. In addition, a numerical study through finite-element modeling was also conducted. A finite-element model was developed and validated to be capable of accurately replicating the experimental results. Subsequent parametric studies using the validated model were performed on the structures with a wide range of dimensions and under various combinations of compression and bending. Based on both experimental and parametric studies results, the applicability of existing design approaches in European and American Standards to the structures subject to combined compression and bending was evaluated. The evaluation results show that the design approaches from the standards, especially the compression and bending interaction relationship, provide conservative strength predictions and can be safely applied to the structures.

An innovative structural modification, top-story softening, is herein proposed in conjunction with an optimally tuned top-floor tuned mass damper inerter (TMDI) for improved serviceability performance in typical core-frame slender buildings with rectangular floor plan susceptible to wind-induced vortex shedding (VS) effects causing occupant discomfort. This is supported through formulating a novel optimal TMDI tuning problem in which TMDI inertial properties, i.e., attached mass and inertance, as well as the lateral top-story stiffness are design parameters aiming to minimize peak acceleration of the highest occupied floor. The optimal TMDI tuning problem is numerically solved for a wide range of design parameters for a 34-story composite core-frame building subject to stochastic spatially-correlated wind-force field accounting for VS effects. A low-order dynamical model capturing faithfully modal properties of the case-study building is developed to facilitate computational work and parametric investigation. It is found that top-story softening reduces attached TMDI mass/weight requirements and inerter force for fixed performance and inertance. It further reduces TMDI stroke and achieves increased robustness to TMDI stiffness and damping properties as well as to the assumed inherent structural damping. It is concluded that by leveraging inertance and top-story stiffness, the proposed solution can efficiently control VS-induced floor acceleration with small additional gravitational (added weight) and horizontal (inerter and damping) forces.

Horizontally curved concrete bridges are widely used in urban viaducts and overpasses all over the world. A box cross-section is often used in curved concrete girders because of its high resistance to both bending and torsion. This study focuses on the development of a new finite element analysis (FEA) methodology incorporating a novel formulation for curved box sections using orthotropic constitutive models for reinforced concrete, along with a layered shell theory approach. In the new approach, the box section is treated as a frame consisting of curved shell elements modeling webs and flanges and curved beam elements in the web-flange junctions. The use of shell and beam elements in the formulation significantly reduces the number of elements needed to model the box-section girder while maintaining the accuracy of the model. A degenerate superparametric shell element with reduced integration is used to avoid shear-locking, membrane-locking, and zero-energy problems. Prestrain effects are considered in the formulation to account for prestressing forces. The simulation results are compared to the available experimental results on four straight and curved, reinforced and prestressed, concrete box-section girders, with good agreement in terms of the deflections, twist angles, and strains in the prestressed reinforcement. Some critical issues in the analysis of concrete box girders, such as postpeak-strength behaviors, distortion of box section, are also discussed.

The instantaneous center of rotation method is presented in the AISC Steel Construction Manual for the design of eccentrically loaded bolted connections. Tabulated values for normalized strengths of bolt groups are provided, and per the classical approach, bolt hole clearance is neglected in the formulation of the results. This study extended the method to consider the effect of bolt hole clearance on the ultimate strength of the bolt group. For vertically applied loads, accounting for the standard hole clearance resulted in, on average, a 2% reduction in the predicted strength of a bearing-type connection when using bolts of diameter less than 25 mm (1 in.) and a 6% reduction for bolts 25 mm (1 in.) diameter or greater. Accounting for the clearance from oversized holes resulted in, on average, a 9%, 14%, and 19% reduction in predicted connection strength for vertically applied load for bolts of diameter less than, equal to, and greater than 25 mm (1 in.) diameter, respectively. The results indicated that neglecting the hole clearance may be unconservative when considering the bearing strength of an eccentrically loaded bolted connection. Based on a probability study, potential factors are proposed to modify the AISC published ultimate strengths. A simplified approach to modeling the slip behavior of individual fasteners using an incremental analysis demonstrated that the slip-capacity of a fastener does not influence the ultimate strength of the connection.

The design of welded rectangular hollow section (RHS) truss-type connections, in which branches are laterally offset from the chord centerline, is not included in any of the current design codes and standards. To provide design recommendations for this type of connection, a series of studies have been performed on cold-formed welded RHS-to-RHS X-connections with branch lateral offset. An experimental study of 14 full-scale laboratory tests has been conducted, including 4 nonoffset control specimens and 10 laterally offset specimens. Two failure mode models representing the behavior of such connections have been proposed, and their validity is evaluated by the experimental results. Following the experimentation, a numerical study with a broader range of parameters was performed on such RHS connections, where nonlinear finite element (FE) models were created and validated against the laboratory tests. Based on the results of the experimental and numerical studies, one of the analytical models—a combined yield-line mechanism—is recommended to be used for the design of laterally offset RHS X-connections.

Ground motion intensity measures (IMs) provide a link between the probabilistic seismic hazard analysis and probabilistic structural response analysis. IMs that are well correlated with the structural response allow an estimation of the seismic response of the structure with low uncertainty (i.e., high efficiency), reducing the computational effort involved in the structural response analysis. In this paper, the efficiency of 10 different IMs for estimating the seismic response of wood-frame single-family houses is evaluated and compared. Six nonlinear models of one- and two-story houses with varying fundamental periods are analyzed. Based on the results, the 5%-damped average spectral pseudoacceleration at a period of 0.16 s is the recommended IM for estimating peak interstory drifts and peak roof accelerations in wood-frame houses. On the other hand, for collapse assessment of wood-frame houses the filtered incremental displacement with one pulse segment, a 4 Hz cut-off frequency, and a period of 0.5 s, is the most efficient IM, followed by peak ground velocity which is also a very efficient alternative. Finally, an expression for the spatial correlation of 5%-damped average spectral pseudoaccelerations is developed for use in regional seismic risk assessments.

This paper presents the development of normalized total force-total impulse (P-I) diagrams for analyzing and designing steel-plate composite (SC) walls to resist far-field blast loads. The P-I diagrams depict contours of constant damage states created using a single-degree-of-freedom (SDOF) model for one-way SC wall panels subjected to uniform pressure loading resulting from far-field blasts. The resistance function for uniform pressure loading was developed using a novel (hybrid experimental-numerical) approach that eliminated the need for specialized testing and loading equipment. The hybrid approach consisted of (1) conducting four-point bending tests, (2) developing and benchmarking three-dimensional (3D) finite-element (FE) models for the tests, (3) using the benchmarked FE models to conduct numerical simulations for uniform pressure loading, and (4) idealizing the resistance function for uniform pressure using a bilinear relationship. The SDOF model and idealized resistance functions were further benchmarked using results from shock-tube tests conducted on SC wall panels. The benchmarked SDOF model was used to conduct parametric analyses leading to the development of ductility-dependent total pressure-total impulse (P-I) diagrams. These P-I diagrams were validated using the experimental results from blast tests and additional results generated using the benchmarked FE models. The P-I diagrams, along with the ductility-dependent damage states, are recommended for the design of SC wall panels subjected to far-field blast loading.

Composite columns consisting of steel hollow sections filled with concrete offer numerous advantages including high fire resistance. However, there are limited provisions for fire design of these columns, and current European code provisions yield unconservative fire resistance in cases of composite columns having relative slenderness greater than 0.5. To overcome the current knowledge gaps, a set of fire-resistance experiments was carried out on a large number of concrete-filled steel tubular columns (CFST). The test variables in the experiments included cross-section type and size, column slenderness, and the support conditions of the CFST columns. From these tests, detailed response parameters, including the evolution of cross-sectional temperatures, axial displacements, lateral deflections, fire-induced axial forces, and failure times, were evaluated. Results from the analysis clearly indicate that cross-sectional shape, support conditions, and column slenderness have significant influence on the fire behavior of CFST columns. Specifically, the axial stiffness reduces the fire resistance of CFST columns, whereas the rotational stiffness increases their fire resistance. Furthermore, CFST columns with an elliptical cross section provide higher fire resistance than equivalent square-shaped or rectangular-shaped columns under certain boundary conditions.

This paper presents an investigation of the seismic performance of concrete columns reinforced longitudinally with steel bars (referred to as UHS-WB bars) that have an ultrahigh strength and a low bond strength. Nine cantilever columns were tested with variables including the type of longitudinal steel reinforcement, the anchorage method for the UHS-WB bars, the axial load ratio, and the shear-span ratio of the columns. The columns with securely anchored UHS-WB bars and shear-span ratios of 2.5 and 3.0 exhibited very stable hysteretic behavior and a mild hardening postyield behavior up to drift ratio of 4%, whereas the lateral resistance of the column with a shear-span ratio of 4.0 had a slight decline beyond a drift ratio of 1.5% due to significant $P\text{-}\delta$ effect. However, all the columns with securely anchored UHS-WB bars had a residual drift less than 0.5% after unloading from the drift of 3%. The stable response and low residual drift can be attributed to the low bond strength, which delayed the yielding of the UHS-WB bars.

An innovative self-centering steel–timber hybrid shear wall (SC-STHSW) system is proposed in this paper. The SC-STHSW system is composed of two subsystems: the posttensioned (PT) steel frame, and the infill light-frame wood shear wall. Slip-friction dampers are used as connectors between the frame and shear wall. A reversed cyclic loading experiment was conducted to investigate the failure modes, hysteretic characteristics, and the loss of posttensioning force in the system. The working mechanism of the subsystems and the interaction between them were explored. Experimental results revealed that the peculiar flag-shaped hysteretic behavior is available in the SC-STHSW system. Under the coupled effects of the PT technology and the slip-friction dampers, the energy dissipation behavior of the system was transferred from the plasticity in primary structural members to the frictional dissipation in the dampers, and the residual deformation of the system was controlled effectively. A detailed numerical model was developed to predict the hysteretic performance of the SC-STHSW system. The model was validated by comparing the experimental and numerical results. This work supports the application of the innovative steel–timber hybrid structural system in practical engineering.

The work presented pertains to the development and application of a damage detection method in bridges by use of distributed fiber-optic sensors. It utilizes the dynamic mode of the Brillouin optical time-domain analysis technique to measure distributed strains and to detect the locations of damage along the entire lengths of bridges. Unlike the current state of practice with distributed sensors, application of the proposed method does not require reference measurements. The practical ramifications of reference-free monitoring of bridges is significant because it eliminates the need for bridge closures. The method described in this article is applicable only when distributed sensors with dynamic measurement capabilities are employed. Two general approaches were considered and tested on two different bridges. Formulation of the method based on calibrated load tests led to a normalized crack index along the entire length of the bridge. The second approach corresponded to formulation of strain differentials and detection of damage under random traffic loads. Analysis of the results by the proposed methods and verification by visual inspections indicated that they were efficient in detecting the majority of anomalies in the bridges.

The paper presents an up-to-date procedure to design shear-resistant concrete flat plates of optimum thickness. Excessive long-term deflection is avoided by the reliable prediction of probable deflection while accounting for the effects of cracking, creep, and shrinkage of concrete and the relaxation of prestressed reinforcement. Safety against shear failure is considered for concrete flat plates without drop panels, beams, or column capitals. Presented analyses satisfy the compatibility of deformations and equilibrium of forces (requirement of ACI 318 code); few empirical provisions in the latest ACI 318 code, not used here, are identified. Empirical procedures aiming at reducing calculations are not needed in practice; thus, they are avoided. The objective is to recommend the most effective analysis in the design of concrete flat plates to avoid shear failure and excessive deflection. Hundreds of experiments done by many researchers are the basis of the depicted design procedure to avoid shear failure. Measurements of bridge deflections calibrate the analytical procedure for predicting long-term deflections; the analysis for long-term deflection assumes that externally applied load is introduced at age $t_0$ and sustained to age $t$; time-dependent changes in strain and deflection are predicted by equations that are based on compatibility and equilibrium principles. Cracking is assumed to have occurred before $t_0$ due to shoring of consecutive upper floors during construction.

Masonry structures constitute an important part of the built environment and architectural heritage in seismic areas. A large number of these old structures showed inadequate performance and suffered substantial damage under past earthquakes. Realistic numerical models are required for accurate response predictions and for addressing the implementation of effective strengthening solutions. A comprehensive mesoscale modeling strategy explicitly allowing for masonry bond is presented in this paper. It is based on advanced nonlinear material models for interface elements simulating cracks in mortar joints and brick/block units under cyclic loading. Moreover, domain decomposition and mesh tying techniques are used to enhance computational efficiency in detailed nonlinear simulations. The potential of this approach is shown with reference to a case study of a full-scale unreinforced masonry building previously tested in laboratory under pseudodynamic loading. The results obtained confirm that the proposed modeling strategy for brick/block-masonry structures leads to accurate representations of the seismic response of three-dimensional (3D) building structures, both at the local and global levels. The numerical-experimental comparisons show that this detailed modeling approach enables remarkably accurate predictions of the actual dynamic characteristics, along with the main resisting mechanisms and crack patterns.

In regions experiencing high-frequency earthquakes, it is necessary to reevaluate the seismic performance of nuclear power plant buildings. In the evaluation of equipment, as well as the structure, the damping ratio of a structure is important. In the present study, to evaluate the damping ratio of walls with limited damage, a shaking table test was conducted for reinforced concrete squat walls with a low aspect ratio. The test variables were the natural frequency of the walls and the type of earthquake (i.e., earthquakes with and without high-frequency contents). The result showed that for a peak ground acceleration of $0.1g$, the damping ratio of the walls was 3.5% for the mean and 0.27 for the standard deviation, while for high-frequency earthquakes, the damping ratio was 14.3% lower (3.0% for the mean). In particular, as the dynamic response amplification increased, the damping ratio decreased; when the dynamic amplification was greater than 1.5, the average damping ratio of the walls was 2.4%.

The state of the practice for the blast-resistant design of structures uses a simplified single-degree-of-freedom (SDOF) analysis and estimates the blast loads assuming reflection from an unyielding rigid surface. Past studies showed that the interaction between the blast wave and the structure might influence the response depending on the blast characteristics and the structural properties. This study proposes a new fluid-structure-interaction (FSI) model and investigates its influence on the blast response of SDOF systems. Phenomena and model characteristics that are expected to influence the FSI response are investigated, and the limitations of past FSI models are addressed. The model includes the effects of aerodynamic damping, structural damping, and the damping caused by FSI that can significantly influence the displacement response. The model can be used to predict the blast response of a SDOF system for a range of shock strengths. The proposed FSI model is verified and validated with other FSI models and experimental studies and shown to predict the FSI response with considerable accuracy. The FSI effects are found to be more dominant in lightweight and flexible members relative to heavy and rigid systems. The study concludes that FSI effects are more significant at smaller-scaled distances ($Z$) at which stronger shocks are encountered. New charts are proposed that can be used to estimate the dynamic response of SDOF systems, including the effects of FSI.

The long-span bridge, characterized by slenderness and flexibility, is particularly sensitive to wind action. Extreme wind events, including typhoons and hurricanes, will threaten the safety and serviceability of long-span bridges. More specifically, long-span bridges usually experience significant vibrations under typhoon events, increasing the risk of serviceability failure and traffic accidents. An efficient way to mitigate the risk of such threats is to predict the typhoon-induced response (TIR). Traditionally, TIR prediction of long-span bridges is usually carried out based on finite-element (FE) simulations. Due to the assumptions in formulating the FE model and establishing the wind load (e.g., boundary conditions, simplified structural elements, stationary aerodynamic wind forces), prediction accuracy is inevitably undermined. In this work, as opposed to traditional FE-based analysis, TIR is predicted in real time from a data-driven perspective. Quantile random forest (QRF) with Bayesian optimization is presented as the data-driven method for probabilistic prediction. A long-span cable-stayed bridge with a main span of $\mathrm{1,088}\mathrm{m}$ is used as a test bed to illustrate the effectiveness of the present method. Other optimization algorithms used with QRF (grid search and random search) and response surface methodology (RSM) are also implemented for comparison purposes. Results indicate that QRF with Bayesian optimization can provide reliable probabilistic estimations allowing for quantification of uncertainty in prediction. It shows superior performance compared with other optimization algorithms and models in terms of accuracy and computational expense. The analysis and predictive framework for TIR are expected to provide insight into data-driven structural wind engineering.

The current study introduces an extension for the multilayered improved applied element method to provide a tool for bonded prestressed concrete structures. In the new extension, a new layer has been implemented to represent the behavior of the prestressing tendon and the transfer of the stresses between the tendon and concrete. Furthermore, an initial load step has been developed to consider the effect of prestressing. During this load step, an initial strain is produced in the tendon layer to represent the effective prestressing. Both material inelasticity and geometric nonlinearity have been considered in the proposed model. Several verification examples under monotonic and cyclic loading are presented to examine the reliability of the model and identifies its limitations. Comparison between the analytical and experimental results has shown good agreement, highlighting the reliability of the new extension.

This paper investigates the experimental behavior of a self-centering (SC) timber brace that employs the resilient slip friction joint (RSFJ) for energy dissipation. Due to the inherent characteristics of the RSFJ, mainly rotational flexibility, it was observed that the brace is susceptible to lateral instability. As will be shown experimentally, the demerit to this lateral instability is the reduction of the bracing capacity in compression, although it is of an elastic type and recovers at the end of unloading. Therefore, this paper aims to prevent the instability issue in the RSFJ-brace system. To do so, a proper framework to predict and quantify the instability is developed, and then a quasi-static test is performed on a small-scale ($1:3$) specimen to evaluate the accuracy of the proposed framework. In order to address the instability problem, the antibuckling tubes (ABT) concept with associated stiffness requirements is introduced in the second part in which the effectiveness is assessed using a quasi-static test on a full-scale specimen. Results indicate that the utilization of the ABT will rule out the possibility of instability.

This paper analyzed damping ratios inferred from 1,335 seismic responses recorded in 154 instrumented buildings in California. These values were inferred using a parametric system identification technique in the time domain, and subjected to a series of reliability screening tests to retain only high-quality data. The resulting damping ratios conformed a data set of 1,037 high-quality values inferred exclusively from the seismic response of buildings, a database several times larger than previous studies of damping inferred from seismic response. The data set was analyzed using a linear mixed-effects statistical model to account for the fact that many of the data points were clustered, because they came from damping ratios in the same building shaken by various earthquakes. It was shown that damping decreases with increasing building height, which is the factor that best explained the relatively large variance observed in the data. Contrary to some previous recommendations, it was found that once the variation with height is taken into account, the primary structural building material is not statistically significant in the damping ratio of buildings subjected to earthquakes. However, when including the combined material and lateral resistant system as a factor in the statistical model, an additional 6% of the variance was explained. Results showed that steel buildings with moment-resistant frames have, on average, a slightly higher damping ratio than those with steel braced frames. The amplitude dependency of damping showed that there was no significant correlation between damping ratio and the overall lateral deformation demand in the building as measured by the peak roof drift ratio for amplitudes typically observed during moderate earthquake motions once a minimum level of amplitude is exceeded.

Predicting the shear strength of structural elements subjected to gravity loads and ground motions is an important component of seismic design. Among all primary structural components, the vital role of columns in load transfer and redistribution, structural stability, and collapse prevention has been well recognized through observations made in the aftermath of past earthquakes. Numerous analytical, numerical, and experimental studies have been conducted to assess the shear strength of RC columns in the past decades. However, there is still a large scatter (i.e., uncertainty) in the predictions of current empirical and numerical models relative to test data. In this paper, novel data-driven models are presented for predicting the maximum shear strength of rectangular and circular RC columns. To this end, two extensive experimental databases for both types of columns were used in the present study. The data were randomly partitioned into calibration and validation sets. The calibration data sets served as the basis for developing linear and nonlinear equations for predicting the ultimate shear capacity of rectangular and circular RC columns through regression analyses. The Monte Carlo method was employed by conducting ${10}^6$, ${10}^7$, and ${10}^8$ realizations to exhaustively examine the optimal parameter space of the postulated equations. The calibrated predictive models were then validated using the validation data sets; and their performances were also compared to existing models. These validation and comparison studies revealed that a new linear model devised and calibrated in the present study achieved very high accuracy, even compared to various nonlinear models considered. It was, moreover, significantly superior to all prior models in predicting the column shear strengths. This linear model, which is based on physical parameters, can therefore be recommended for engineering practice.

The paper deals with the dynamic characterization of a reinforced concrete (RC) frame school building in central Italy before and after the seismic retrofitting, obtained by coupling the building with an innovative patented seismic dissipative protection system. Before the retrofit, ambient vibration tests were performed to evaluate frequencies and mode shapes for developing finite-element (f.e.) models describing the school dynamic behavior in operational conditions. Several finite-element models with increasing level of detail are presented, from the bare frame model, based on the assumptions and simplifications usually adopted for design purposes, to an upgraded model taking account of secondary and nonstructural elements (e.g., internal and external walls, screeds, roofing, floor tiles, and plasters) as well as the interaction between structure and retaining walls. The latter was used to develop the design model of the seismic retrofitting system, which aims to assure the immediate occupancy of the building in the case of severe earthquakes limiting damage to nonstructural components. Tests were repeated after the retrofit to check consistency with numerical design predictions. Comparisons between experimental and numerical modal parameters are shown discussing the usefulness of ambient vibration tests.

Architectural facades including balconies, mullions, shading boards, and ribs are widely used outside of tall buildings for the purpose of aesthetics and function. And these facades will affect the wind loads of tall buildings, such as the local wind pressure and aerodynamic force. Thus, to study the influence of architectural facades on wind loads of tall buildings is an important task in wind resistant design. However, most studies focus on the effect of the architectural facade on the local wind pressure using wind tunnel experiments. In the present paper, multiple point synchronous pressure measurements and high-frequency force balance (HFFB) experiments for tall buildings with various architectural facades are conducted to study the influence of different horizontal facades and vertical facades on the local wind pressures and the aerodynamic forces. The results show that the facade may have a significant influence on the local wind pressure and aerodynamic force, and the facade itself may suffer from the larger force.

A simplified method is proposed for evaluating the stability of multistory, steel, semibraced, and unbraced frames with semirigid connections. The proposed method decomposes a frame into individual stories and evaluates the lateral stiffness of each story via the story-based stability approach with explicit, closed-form solutions. Lateral sway instability occurs when the lateral stiffness of any story diminishes to zero, and the story for which this occurs can be considered the weakest story in the frame. The results of the proposed method are theoretically verified via comparison to the results of finite-element analyses. The use of the proposed decomposition method requires assuming the buckled shape of the frame, which is shown to provide satisfactory approximations of critical loads for engineering practice. Parametric studies are conducted to assess the sensitivity of the results to the corresponding buckling shape parameters. The assumption of asymmetric buckling, which is generally consistent with the sway buckling mode in semibraced frames, produces reliable results in the proposed decomposition method.

An experimental program investigating the behavior of glued laminated timber (glulam) assemblies with various bolted connections subjected to simulated blast loading was undertaken. A total of 14 full-scale tests on $137\times 267\text{-}\mathrm{mm}$ glulam members with idealized and realistic boundary conditions were carried out using a shock tube apparatus capable of simulating the effects of far-field blast explosions. Full-scale glulam specimens with bolted connections designed to yield in bolt bending performed better than those that were overdesigned. Proper detailing of the bolt group geometry was found to be sufficient to achieve the desired failure sequence. Reinforcement with self-tapping screws changed the failure mode from that of splitting to a combination of bolt yielding and wood crushing and provided additional ductility in the assembly. A two-degree-of-freedom blast analysis was found to adequately capture the system response with reasonable accuracy. An investigation of the current Canadian blast design provisions showed that the design approach does not allow for energy dissipation in the assembly. An approach is proposed that requires more stringent provisions for the design of brittle failure modes in connections and ensures that ultimate failure will occur in load-bearing timber elements.

This paper investigates a new simulation framework for analyzing structural systems with unconventional complex materials under extreme loading conditions. The new experimental-numerical simulation method, named material testing–integrated (MTI) simulation is capable of incorporating the physical behavior of complex materials into the numerical simulation of large structural systems in real-time or nonreal-time modes. In this study, the new simulation method is applied on a reinforced concrete (RC) frame rehabilitated by applying active confinement on the columns using external shape memory alloy (SMA) spirals. Two MTI simulations are conducted to assess the impact of SMA confinement on the frame when: (1) SMA is applied as a repair measure (i.e., on a damaged structure), and (2) the ambient temperature drops significantly. Simulation results indicate that the SMA spiral is effective in maintaining the lateral force capacity of a damaged frame. However, its effect slightly decreases at extremely low temperatures.

This paper presents an experimental investigation to study the influence of the type of end connections as well as the detailing of end-protected zones on the seismic performance of special concentrically braced frames (SCBFs). Depending on the plane of the brace buckling and the location of plastic hinges, three types of end connections are considered in this study: the in-plane buckling brace system, the out-of-plane buckling brace system, and the direct-connection brace system. Five large-scale braced frame subassemblages are tested under quasi-static reversed cyclic loading. The main parameters studied are the energy dissipation, postbuckling strength, fracture ductility, and failure modes of test specimens. Test results showed that the fatigue performance of the brace specimen is increased by increasing the flexibility of the secondary hinges and a higher fracture ductility can be achieved for the restraint-free rotation of hinge plates. The higher flexibility of the secondary hinges resulted in the spreading of inelastic strain along the brace length. Lower postbuckling strengths of the braces resulted in higher fracture ductility. Test results highlighted the importance of the end-protected zones in the prediction of the fracture ductility of braces for the collapse-performance assessment of the braced frames. Based on this study, recommendations on the design and detailing of end-protected zones have been proposed considering the critical limit states to achieve the desired yield hierarchy of SCBFs.

This paper presents recent research carried out at the University of Sydney on the full-range behavior of top-and-seat angle connections. A total of 18 tests were conducted, covering two connection configurations and three loading conditions, including bending, combined bending and compression, and combined bending and tension. The highlights of the experimental program include the following: (1) all connections were tested to their complete failure, thereby investigating the full-range behavior of the connections, including initial stiffness, ultimate bending strength, ductility, and failure mode, and the detailed behavior of the top flange cleat component; and (2) multiple tests were carried out on nominally identical connections to examine the variability of joint behavior, providing valuable information for estimating the uncertainties in joint properties due to the random variation in geometrical and material properties, including imperfections introduced during fabrication. Conclusions were drawn from the experimental results on the applicability and accuracy of the Eurocode 3 Part 1-8 provisions for calculating the initial stiffness and ultimate strength of top-and-seat angle connections. The results indicated that the Eurocode 3 model significantly underestimates the connection strength by more than 80% because of the conservative strength prediction of the top flange cleat component. To overcome this limitation, a new mechanical model was developed for the top flange cleat component to more accurately predict its full-range behavior, from initial linearity to complete failure. The model reflects the real deformation pattern of a flange cleat by capturing the development of four plastic hinges in the cleat while remaining simple and applicable to hand calculation. The model was applied to the tested connections and indicated a conservative and reasonably accurate strength prediction with substantial improvement from the current Eurocode 3 model.

A dynamic experiment of progressive collapse constitutes the basis of a collapse-resistant analysis. To achieve broad applicability and avoid superfluous influencing factors, two representative substructures extracted from long-span single-layer spatial grid structures were tested using a quick-loading system. The strain and displacement results of the specimens were analyzed, as well as the collapse-resistant mechanisms. The dynamic performance of a full-scale Kiewitt dome was investigated using the hybrid finite-element (FE) model. Finally, a novel cable-reinforced Kiewitt dome is proposed to improve the collapse resistance of Kiewitt domes. The results show that the tests and associated analyses contribute to establishing a database of benchmark models for collapse-resisting simulation of long-span single-layer spatial grid structures. The FE results are well-validated by the test results. The time history of the loading with a suddenly applied load of 1,000 kg for S-10 is similar to the time history of the resistance in a compression mechanism. Owing to the geometric nonlinearity, the time history of the resistance for the catenary mechanism is asymmetrically distributed based on the final equilibrium state. The dynamic performance of long-span single-layer spatial grid structures is significantly affected by the duration of the suddenly applied load. The maximum displacement of the novel cable-reinforced Kiewitt dome is substantially reduced, and the maximum stress is smaller than the yield stress of steel. The superiority of the cable-reinforced Kiewitt dome is therefore demonstrated.

In steel truss bridges, severe damage due to corrosion at gusset plate connections has been widely reported. This study investigated the effectiveness of a repair method using carbon-fiber-reinforced plastic (CFRP) sheets for corroded gusset plate connections. Loading tests were conducted with a model approximately 50% of the size of actual gusset plate connections and a corrosion level of approximately 50% of the gusset plate thickness. Further, loading tests were carried out by varying the area, direction, and location of the bonded CFRP sheets. Results showed that the proposed repair method recovered the load-carrying capacity and improved the deformation performance of the corroded gusset plate connections. Three-dimensional finite element (FE) analyses, which considered the nonlinear properties of materials, anisotropic performance of CFRP sheets, and bond-slip model of the polyurea putty layer inserted between the corroded gusset plate and CFRP sheets, were implemented to validate the experimental results. By varying the bond-slip properties of the polyurea putty layer within the fluctuation range of measured data, this study accurately reproduced the experimental results and clarified the polyurea putty layer’s influence on the load-carrying capacity, deformation performance, and failure behavior of the corroded gusset plate connections bonded to CFRP sheets.

Nonlinear time-history analysis is becoming a standard procedure for evaluating the seismic performance of structures. The current ASCE 7-16 allows practitioners to perform it when the acceleration demands of nonstructural components (NSCs) are required. However, the code in this version omits any suggestion regarding the methodology that should or could be used to represent the structure as a mathematical model. This investigation evaluated the acceleration demands in rigid and flexible nonstructural components using five different assessment methodologies that vary from a detailed concentrated and distributed plasticity model to a very simple model. Nonlinear static and dynamic analyses were performed on 2-, 4-, 8-, 12- and 20-story special steel moment frames to evaluate the effects that mathematical models have on the structure´s seismic response and acceleration demands on NSCs. Although results showed that detailed models are the only ones that adequately can capture structure drift deformations, it was found that even the simplest nonlinear model evaluated the acceleration demands correctly in NSCs.