Journal of Structural Engineering

This paper presents full-scale experiments and computational analyses on exposed column–base plate connections with ductile anchors. The aim is to examine the seismic performance of these connections for their prospective use as weak bases, wherein steel moment frames are designed to concentrate inelastic rotations in the base connections rather than in the connected columns. The connections feature upset thread anchor rods in which the threads are milled to a smooth shank, providing a designated stretch length over which inelastic deformations may be concentrated. The shank is frictionally isolated from the footing using polyethylene tape. The four full-scale experiments investigate the effects of axial force, rod diameter, and rod material grade. The test specimens withstand (without anchor rod failure) the application of two Applied Technology Council–the Joint Venture partners of the Structural Engineers Association of California, the Applied Technology Council, and the Consortium of Universities for Research in Earthquake Engineering (ATC-SAC) protocols applied consecutively (each to drift amplitudes of 5%), followed by additional cycles to 6.5% drift amplitude. Complementary line element–based and continuum finite-element simulations are conducted to examine to what extent the experimentally observed response may be generalized to untested configurations. Implications for design are summarized, along with the limitations of the study.

This study evaluated the performance of smart steel moment-resisting frame structures (MRFs) equipped with nickle titanium shape-memory alloy (NiTi SMA) connection systems subjected to blast overpressure. A total of five NiTi SMA–based connections were designed conforming to current European standards, and their numerical models were developed. To study the effect of number of parameters, e.g., section profiles, bolt diameter, and bolt preload, a parametric study has been conducted on NiTi SMA–based connections. The numerical models were validated against experimental data, and key design procedures have been proposed. A simplified Kingery blast calculation framework was adapted to determine the blast reflected overpressure profile. The strength of the NiTi SMA bolts and steel components were adjusted due to a high strain rate of blast loading. Four MRFs equipped with a NiTi SMA–based connection were designed with different heights. Global-level transient analyses were performed on the MRFs subjected to blast overpressure. The results showed that in addition to relatively large maximum interstory drift ratio, the NiTi SMA–based connections significantly reduced the residual interstory drift ratio compared with the steel bolted connection system counterpart. The results also revealed that the proposed key design procedures are essential to emphasize the role of NiTi SMA bolts.

The complex behavior of high-strength steel staggered-hole bolted connections failing in block shear with a combination of tension and inclined shear behavior was studied in this work. In particular, the location of the fracture paths in the staggered zones correlated with the angle of the staggered holes instead of appearing on the centerline between the staggered holes. Furthermore, the nominal shear strength of the staggered-hole bolted connections in the staggered paths was affected by the combination of shear and tension rupture, accounting for two components, which were the shear strength on failure paths parallel to the force and the tension strength on the segments perpendicular to the force. Consequently, a design equation for block shear strength with staggered holes was proposed to account for the combined actions. It demonstrated better correlation with the experimental results than the predictions from current design standards. A total of 88 specimens with two G450 sheets with thicknesses of 1.9 and 2.4 mm were modeled by means of a finite-element model validated against the actual tests to achieve reliable data using a parametric procedure. In addition, four different types of configurations, including not only four holes but also three and five holes were modeled to investigate the effect of the inclined shear and tension zones on the block shear strength and behavior of the connections. The large data set was used for the verification procedure of the proposed formula.

Despite ongoing research efforts aimed at understanding the structural response of ultrahigh-performance concrete (UHPC) beams, there are very limited provisions for structural design of UHPC beams, specifically under flexure. To address the current limitations in design provisions for UHPC beams, which notably hinder the applicability of UHPC in concrete structures, it is essential to develop simplified design methodologies that can optimize the superior range of properties offered by this new class of material. In this study, a machine learning (ML)–based approach for predicting the flexural capacity of UHPC beams was developed. ML algorithms such as support vector machine regression (SVMR) and multigene genetic programming (MGGP) were applied to analyze data and observations collected from large set of tests on UHPC beams with different geometries, fiber properties, and material characteristics. SVMR was applied to predict the flexural capacity of UHPC beams, whereas MGGP was employed to derive a simplified expression, through data-driven analysis of actual test data, for predicting the flexural capacity of the beams. A parametric study was also performed to validate the proposed approach with varying input parameters. The results indicated that the proposed data-driven approach using ML was effective in predicting the flexural capacity of UHPC beams with different material and configuration characteristics, paving the way for the development of guidelines for the design of UHPC beams. The results of this comprehensive analysis showcase the merit of employing ML in structural engineering applications and thereby promoting the applicability of UHPC in concrete structures.

To fully recognize the load-resisting mechanisms of post-tensioned concrete (PC) structures with realistic boundary conditions against disproportionate collapse, four beam-column subassemblies were extracted from a prototype building and the side columns and joints were reproduced to reflect the actual boundary condition. The parametric analysis was conducted, including location of the removed column (middle or penultimate) and strand profile (straight or parabolic). In addition, two RC counterparts were tested as a control group. Test results indicate that the unbonded post-tensioning strand (UPS) was able to enhance the structural robustness by increasing compressive arch action capacity of RC beams and developing catenary action. Compared with RC specimens, both PC specimens achieved much higher load resistance; herein, the PC specimen with straight strand profile obtained the highest load resistance due to two strands used, while the PC specimen with parabolic profile had higher deformation capacity. However, the existence of UPS increased the tensile force demand to the side column, leading to the flexural tension failure of the side column when the loss of a penultimate column was considered. Finally, an analytical study was carried out to quantify the load resistance from each dominant load-resisting mechanism.

This paper addresses the analysis of planar frames with stiff semirigid joints. If they are stiff enough, a concept which is discussed with respect to the local stiffness of the neighboring beams and columns as well as the global flexibility of the whole structure, the joints can be modeled as fully rigid. This makes the structural analysis easier for practitioners who sometimes are reluctant to perform a structural analysis accounting for the semirigidity of the joints. If joints cannot be classified as fully rigid, a more sophisticated structural analysis is required, according to current practices and standards. This paper developed an asymptotic analysis of the static structural response of frames with stiff (but not infinitely rigid) joints. It was demonstrated that the small deformability of the joints in rotation can be taken into account by analyzing the structural response of the fully rigid frame as the sum of two load cases: (1) the actual loading on the considered structure, and (2) an additional virtual loading which takes the (small) flexibility of the joints into account and which is expressed as a function of the response of the structure to the actual loading. The proposed method therefore avoids the consideration of the semirigidity of the joints in a structure when they are not perfectly rigid. It is similar to other practices in the field of structural engineering such as the use of equivalent loads to account for small initial imperfections or to deal with a second-order analysis. The method was derived formally and validated with several examples with increasing complexity. The method offers new perspectives on the classification of joints in a very simple and general way; it also might inspire similar approaches for structural stability analysis of structures with almost rigid or almost hinged connections.

Temperature-induced responses have been found to be sensitive to changes in bridge properties. Accordingly, researchers have sought to develop temperature-response mappings that could be used in assessing bridge conditions; to date, obtaining sufficiently precise mappings analytically has proven intractable. Alternatively, numerous researchers have directly developed mappings between temperature and the associated responses using measured data. However, temperature-induced responses are a function of the temperatures throughout the entire bridge, and such spatial temperature distributions using a limited number of sensors are challenging to capture, particularly for steel truss bridges, due to the large number and variety of structural members. Mappings that have been obtained are generally a function of the long-term fluctuations, corresponding to daily variations; the short-term fluctuations (i.e., higher-frequency components) in temperature data are neglected. This paper first proposes that the relationship between increments in temperature and the associated increments in responses can be used as a surrogate to assess the bridge performance. Simulation results show that the statistical distribution of the error between measured and predicted response increments can be used for identifying abnormal structural behavior. Then, various mappings for both displacement and strain increments are explored and verified using field monitoring data. The mapping with all temperature sensors performs the best; principal component analysis (PCA) can effectively reduce the dimension of input without compromising accuracy. In addition, the recorded time of temperature data is validated to be a useful indicator of the spatial temperature distribution in bridges, which can be used to improve the performance of the mappings when the bridge has only a few temperature sensors. These findings provide an improved approach for mapping the relationship between increments in temperature to increments in temperature-induced responses that shows promise for identifying abnormal bridge behavior.

Concrete anchors in base plate connections may develop large bending moments under shear. The moments were shown to be proportional to the length of laterally unsupported anchor shafts, referred to as the effective exposed length in this paper. This length includes an apparent exposed length measured from bottom of plate or leveling nut to the concrete surface in a stand-off connection and a crushed concrete depth below concrete surface. The paper reports a total of 12 shear tests of single anchors and 101 finite-element analyses to determine the factors critical to crushed concrete depths, including concrete and anchor materials, anchor diameters, and stand-off heights. The study shows that the crushed concrete depth increases with an increase in the diameter of an anchor and its ultimate tensile strength, and decreases with an increase in concrete strength and the stand-off height. Equations are proposed to estimate the effective exposed lengths and the shear capacities of anchors governed by steel. The design equations reasonably predicted the shear capacities of 153 experimental tests. The proposed concept of crushed concrete depths facilitates future research on the shear capacities of anchors governed by steel, although other models are available in the literature to explain the existing tests.

Adaptive reliability analysis methods based on surrogate models, especially kriging, have been successfully implemented in many problems. However, the application of kriging is limited to low-dimensional problems with noncategorical performance data. Support vector machine (SVM), by contrast, addresses these limitations, but its application in reliability analysis faces several challenges with regard to robustness, accuracy, and efficiency. This study proposed a new adaptive approach based on probabilistic support vector machine for reliability analysis (PSVM-RA). Different from existing methods that only select training points in the margin of the SVM, the proposed method adopts a new learning function that considers the wrong classification probability for each realization and maximizes the potential for new information offered by a candidate sample for the training set. Moreover, the upper bound of the error that is introduced by the SVM in estimating the failure probability is derived based on a Poisson binomial distribution model considering the likelihood of wrong classification for all the points in the margin of the SVM. This upper bound of error was used in the proposed framework as a stopping criterion to guarantee the desired accuracy. Three numerical examples and an engineering application regarding the wind-reliability analysis of transmission towers were investigated to demonstrate the performance of the proposed method. It was demonstrated that PSVM-RA can provide robust estimates of failure probability when other state-of-the-art methods fail. Moreover, it offers a balance between efficiency and accuracy.

The objective of this study was to monotonically test two $7.32\times 7.32\text{-}\mathrm{m}$ ($24\times 24\text{-}\mathrm{ft}$) cross-laminated timber (CLT) diaphragms designed using the provisions of ANSI/AWC 2021 (AWC. 2021. Special design provisions for wind and seismic. ANSI/AWC SDPWS-2021, Leesburg, VA: AWC). Each diaphragm used twelve $1.22\times 3.66\text{-}\mathrm{m}$ ($4\times 12\text{-}\mathrm{ft}$) CLT panels and plywood splines or glulam beams at panel shear connection locations. Diaphragms were tested in simple-span bending in general accordance with ASTM E455 (ASTM. 2017. Standard test method for static load testing of framed floor and roof diaphragm constructions for buildings. ASTM E455-2017. West Conshohocken, PA: ASTM), used 8d common [$3.3\times 63.5\text{-}\mathrm{mm}$ ($0.131\times 2.5\text{-}\mathrm{in.}$)] nails for panel-to-panel spline connections used proprietary $7.9\times 200\text{-}\mathrm{mm}$ ($5/16\times 7\text{-}7/8\text{-}\mathrm{in.}$) screws for panel-to-beam connections. The calculated allowable seismic shear design capacity for both configurations, based on the panel shear connections, was 60.5 kN (13.6 kips) per reaction. The diaphragm tested with load applied parallel to the long dimension of the CLT panels failed due to spline nail withdrawal at 4.0 times the allowable seismic design capacity. The diaphragm tested in the orthogonal orientation did not fail at the safe working capacity of the steel test frame, which was 6.0 times the allowable seismic design capacity. Although this testing provided empirical verification that the SDPWS design provisions met the minimum strength target underlying the design requirements, it also identified opportunities for potential future research to reduce design conservatism. Experimental results from a series of diaphragm connection tests correlated to the connections used in the full-scale diaphragm testing are described in the Part 2 companion study (Line et al., forthcoming).

The objective of this study was to conduct tests on diaphragm connection configurations that either matched or were similar to those used in the full-scale diaphragm tests described in the Part 1 companion study (Line et al. 2022). The goal was to quantify their lateral load-deformation performance as an isolated assembly to assist in further understanding the measured full-scale diaphragm behavior. Diaphragm connection configurations tested include the custom steel tension strap, panel-to-beam screw connections, and panel-to-panel nailed spline connections. Withdrawal strength, dowel bending yield strength, dowel bearing strength, and fastener dimensions, as well as the oven-dry specific gravities of the cross-laminated timber (CLT) and glulam materials used to fabricate the full-scale diaphragms were also quantified. The diaphragm connection lateral load test data for the proprietary screws and spline nails met or exceeded their target nominal capacities calculated in accordance with ANSI/AWC 2018 (AWC. 2018. National design specification for wood construction. ANSI/AWC NDS-2018, Leesburg, VA: AWC) for each connection configuration. Additionally, the overstrength was well aligned with the overstrength performance observed in the full-scale diaphragm tests. The dependence of full-scale diaphragm strength on the strength of its connections and the large overstrength in panel-to-beam screw connections quantified in this study highlight an opportunity to achieve more efficient designs with fewer screws. To do so would likely require the allowable lateral design strengths for screwed connections to be established empirically or by explicit consideration of various connection failure limit states.

Reinforcing old bridges with corrugated steel (CS) is gaining interest due to outstanding reinforcement effects and relative ease of implementation. The approach consists of positioning the CS member under an old bridge and joining the two components by postcast concrete. However, the current design approach ignores the supporting effect of postcast concrete and the old bridges, which is overly conservative. This paper studies experimentally the static performance of the reinforced concrete (RC) arches reinforced with CS, mainly considering the influence of damage degree of the original structure. Two RC arches were prepared and loaded up to 60% and 100% of their ultimate bearing capacity, respectively. After reinforcing and reloading, failure modes, bearing capacity, and ductility of the reinforced specimens were obtained. The results show that when reinforcing the arches with CS, the ultimate bearing capacity increased by 172.8% and 194.0%, respectively. Comparison of the two reinforced specimens shows that the damage degree has only a small effect (8.2%) on the ultimate bearing capacity. Besides, the original structure, postcast concrete and CS were well bonded based on the strain analysis, proving the reinforced structure has the composite effect.

The seismic vulnerability of existing RC framed buildings in seismic-prone areas requires affordable and practice-oriented solutions for their retrofitting. In this paper, the authors present a retrofitting solution for RC buildings based on the combined use of cross-laminated timber (CLT) panels and asymmetric friction connections (AFCs). The AFC connection is activated when the force level reaches the design threshold. The energy dissipation of the AFC increases the structural dissipation capacity and reduces the displacement demand. This research presents the outcomes of an experimental campaign on selected prototypes of these AFC connectors. The authors assess their dissipative capacity from cyclic load tests in four different connector arrangements and examine the contribution of aluminum shim layers. The first results highlight the significant dissipation potential of the AFC, although they also provide evidence of the notable sensitivity on the design and constructive details. The authors present a modeling approach to simulate the experimental results.

Catenary action is recognized as one of the main resistance mechanisms for typical steel frame structures against progressive collapse. As a result of catenary action, large rotation, and axial tension demand are applied to the steel connection. Since the failure of the steel connection under catenary action is dominated by the tensile fracture of the steel component, the ultimate rotation capacity of a steel connection is controlled by the ultimate deformation capacity of the steel component. This paper proposes a calibration method for web cleat connections to evaluate the rotation capacity under column loss scenarios. The proposed method incorporates both component tests of bolted angle under tensile load conditions and structural tests of web cleat connections under column loss scenarios. First, the ultimate deformation capacity of bolted angle is developed based on the component test data. Next, the relationship between the ultimate deformation capacity of the component and the rotation capacity of the steel connection is investigated. An analytical model is established to evaluate the rotation capacity of a steel connection. Finally, based on the experimental tests of web cleat connections under simulated column loss scenarios and component tests of bolted angles, the likelihood function and the prior density function of the model parameters are developed. The component tests and structural tests are combined using Bayesian theory and the Markov chain Monte Carlo simulation method. Comparison studies show that the developed model achieves higher model accuracy against the existing equations. The proposed calibration method provides new insight into the development of the rotation capacity of steel connections, especially when the experimental test of steel connections against progressive collapse is limited.

Large single-column billboards are vulnerable to wind hazards. The current building codes for the wind-resistant design of single-sided billboard structure is not applicable to multisided billboards. Therefore, there is a need to carry out comprehensive studies of the wind-resistant design of multisided billboards. This paper presents a comprehensive study of the wind loads and wind-induced responses of monopole three-sided billboard structures based on a series of wind tunnel tests. The aerodynamic testing was performed on a rigid billboard model to measure the wind-induced pressure on the rectangular billboard plates. The wind loads on the billboard in alongwind, crosswind, and torsional components were quantified. In addition, aeroelastic testing was performed for an aeroelastic model of the same structure to measure the dynamic wind-induced responses at the base of the supporting column. The stress at the base of the supporting column was calculated based on the measured responses. The result shows that the normal stress under the alongwind bending moment has a significant contribution to total normal stress, and the shear stresses caused by torsion and shear force can be ignored when calculating von Mises stress. The most unfavorable wind direction is 0° in terms of maximum von Mises stress. A theoretical framework is proposed to estimate the alongwind response in the 0° wind direction with the consideration of aerodynamic damping, and the framework was validated using the measurements. The results revealed the importance of the consideration of the aerodynamic damping and the resonant component. This study provides a comprehensive discussion of the wind loads and the analytical approach for the prediction of the wind-induced responses of monopole three-sided billboard structures, which can be used to design and assess the vulnerability of monopole three-sided billboard structures to wind hazards.

A test program on cold-formed steel (CFS) laced columns fabricated using plain channels has been presented in this study. Twelve specimens with single and N-type lacing configurations were fabricated. The lacing plates and the end-plates were connected to the chords by using self-drilling screws. The effect of critical parameters, like lacing slenderness and transverse chord spacing, on the performance of laced columns under concentric axial loading was investigated. The aspect ratio of the built-up section of the specimens varied from 0.75 to 1.25. The relative slenderness of the unsupported chord (with respect to the global slenderness of the column) ranged from 0.31 to 0.87 in single-laced columns and 0.15–0.44 in N-type laced columns. The performance of the specimens was assessed in terms of their failure modes, peak strengths, and load-displacement trends. Lastly, the strength estimations from both the current American (AISI S100-16) and European (EN1993-1-3) standards were evaluated by comparison against the test strengths. It was noted that both these codes overpredicted the strength of the laced column specimens by up to about 25%. The modified design rules catering to both American (AISI S100-16) and European (EN1993-1-3) standards, previously proposed by the authors for CFS battened columns, were assessed, and their strength predictions were found satisfactory for both types of lacing configurations. The reliability index determined using the modified design rules was approximately equal to three, indicating high reliability.

Base isolators and fluid viscous dampers are viable protective devices that have been commonly considered in the seismic protection of civil engineering structures. However, the optimal design of these devices remains a tedious and iterative undertaking due to the uncertainty of ground motions, the nonlinear behavior of the structure, and its change of dynamic characteristics (i.e., effective stiffness and damping ratio) under each new design. The optimal design problem becomes more challenging concerning a multiresponse bridge system where conflicting damage potential is often expected among multiple bridge components (e.g., column, bearing, shear key, deck unseating, foundation). In this respect, this study develops a risk-based optimization strategy that directly links the expected annual repair cost ratio (ARCR) of the bridge to the design parameters of base isolators and fluid dampers. This strategy is achieved by devising a multistep workflow that integrates a seismic hazard model, a design of experiment for bearings and dampers, a logistic regression towards parameterized component-level fragility models, and a bridge system-level seismic loss assessment. The developed ARCR is parameterized as a convex function of the influential parameters of seismic protective devices. As such, optimal bearing and damper designs can be pinpointed by directly visualizing the global minimum of the parameterized ARCR surface. The optimal design is carried out against a typical reinforced concrete highway bridge in California that is installed with the fluid dampers and three types of widely-used isolation bearings—the elastomeric bearing, lead-rubber bearing, and friction pendulum system. It is shown that optimal design parameters can be obtained to significantly reduce the expected ARCR of the bridge, whereas combining optimally designed bearings and dampers can provide the minimum seismic risk.

The retrofit of wood-frame residential buildings is a relatively effective strategy to mitigate damage caused by windstorms. However, little is known about the effect of modifying building performance for intense events such as a tornado and the subsequent social and economic impacts that result at the community level following an event. This paper presents a method that enables a community to select residential building performance levels representative of either retrofitting or adopting a new design code that computes target community metrics for the effects on the economy and population. Although not a full risk analysis, a series of generic tornado scenarios for different Enhanced Fujita (EF) ratings are simulated, and five resilience metrics are assigned to represent community goals based on economic and population stability. To accomplish this, the functionality of the buildings following the simulated tornado is used as input to a computable general equilibrium (CGE) economics model that predicts household income, employment, and domestic supply at the community level. Population dislocation as a function of building damage and detailed sociodemographic US census-based data is also predicted and serves as a core community resilience metric. Finally, this proposed methodology demonstrates how the metrics can help meet community-level resilience objectives for decision support based on a level of design code improvement or retrofit level. The method is demonstrated for Joplin, Missouri. All analyses and data have been developed and made available on the open-source IN-CORE modeling environment. The proposed multidisciplinary methodology requires continued research to characterize the uncertainty in the decision support results.

This study proposes an innovative type of simple connection utilizing power-actuated fasteners to join a cold-formed steel channel to a rectangular hollow section column via a web-side plate or a T-section. An experimental program composed of 26 specimens was carried out to investigate the behavior of the connections under the combination of shear and rotation. The experimental results are discussed in two limit states including bearing and pull-out by shear. An analytical model is proposed to predict the shear strength of the connections based on the provided information of vectorial force at a fastener, displacement, and rotation at the connections. The proposed model yields a conservative prediction for the tested connections with a mean test-to-prediction ratio of 1.05 and the coefficient of variation of 6% or 9%, depending on the limit state. A design example is provided to illustrate the implementation of the proposed model in practice.

The legacy of structural artist Félix Candela is defined by his integration of thin hyperbolic paraboloid (hypar) shells within architecture across the Americas. One such form is the inverted umbrella, arising from the merger of four straight-edged hypar quadrants. The strength and elegance embodied by this geometry facilitated the recent conceptualization of kinetic umbrellas as an adaptable alternative to conventional floodwalls against surge-induced coastal inundation. Although the conceptual feasibility of such structures under hydrostatic inundation has been ascertained, their performance under combined surge and wave loading remains unknown. This paper used a three-dimensional (3D) numerical scheme integrating smoothed particle hydrodynamics with finite-element modeling for the structural analysis of kinetic umbrellas under the hydrodynamic regime. The technique was validated via dam-break testing involving 3D-printed specimens, and through empirical wave pressure formations at full scale. The behavior of kinetic umbrellas subject to surge and wave impact imparted by Hurricane Sandy (2012) at Monmouth Beach, New Jersey, was evaluated across different hypar geometries and angles of wave attack. Results showed the introduction of hypar geometry significantly enhances structural performance such that a 100-mm-thick umbrella successfully can resist hydrodynamic wave forces accompanying 2.7 m of inundation from landfalling hurricanes. Ultimately, this paper illustrates a creative yet practical structural engineering solution for mitigating the effects of climate change in coastal communities.

A series of acoustic propagation experiments was conducted in the University of Florida Boundary Layer Wind Tunnel (UFBLWT) to investigate tornadic infrasound propagation in the turbulent atmosphere. A synthetic acoustic wave was generated within a boundary layer wind field using a speaker, and distorted by the surrounding turbulent atmosphere as it propagated along the UFBLWT fetch where it was measured by an acoustic microphone 22 m downwind of the speaker. The wind tunnel operating speed and the configuration of the mechanical turbulence generating roughness elements were varied between experiments to alter the turbulence characteristics and thus the distortion of the acoustic wave. The wind field turbulence data were obtained by three Cobra probes mounted on an actuated and automated gantry. The turbulence-induced distortion of the acoustic wave was captured by analyzing the signal at its source and as-measured downwind. Data were characterized, organized, and curated into four stages.