Journal of Structural Engineering

This paper presents the experimental results from nine full-scale concrete-filled double-skin tubular (CFDST) beam-columns. The test specimens exploited two fabrication strategies, featuring either hollow steel inner skins with corrugated geometry or ultrahigh-strength steel corner tubes to enhance the seismic performance of noncompact CFDST beam-columns for potential use in low-to-moderate seismicity regions. The effects of loading sequence, axial load ratio, and cross-sectional geometry were investigated. The experimental results suggested that the current AISC specification may be used to predict the axial strength of composite members with a relatively good accuracy. In the postbuckling range, conventional CFDST beam-columns and those with corrugated inner skins are prone to fracture at the corner welds of the built-up cross section. However, the latter exhibited up to two times larger drift capacities than conventional CFDST counterparts prior to losing axial load carrying capacity. Noncompact beam-columns retrofitted with ultrahigh-strength steel corner tubes exhibited a 4% lateral drift demand without experiencing more than 25% flexural strength loss. The presence of ultrahigh-strength steel increases the plastic hinge length of CFDST beam-columns by up to four times relative to CFDST beam-columns with corrugated inner skin, regardless of the employed loading history.

A common approach of blast-resistant design for external detonation is to design the envelope of a structure to absorb most of the applied blast load impulse, by exploiting the mechanisms of plastic energy absorption and inertial resistance, thus minimizing damage on the supporting structure. The influences of these two mechanisms on the response of the supporting structure are investigated in the present study through a dimensionless, two-degree-of-freedom (2DOF) model representing the cladding (first DOF) and the supporting structure (second DOF). The 2DOF model is validated with nonlinear dynamic finite element analyses of a specific cladding-to-framing system and by comparing 2DOF results with experimental and analytical results found in the literature. Using the validated 2DOF model, the effects of the cladding’s mass, stiffness, ultimate resistance, and ductility are explored with parametric studies for a wide range of parameters. The differentiating factors between the corresponding spectrum regimes (impulsive, dynamic, and quasistatic), where the two mechanisms are activated, are thoroughly examined, and their limits are highlighted. It is shown that the plastic energy absorption mechanism is activated in specific spectrum regimes, through low yield strength and high ductility in the cladding, whereas the inertial resistance mechanism can be activated over the entire spectrum, by applying increased mass and/or low stiffness to the cladding.

This paper presents experimental testing on glulam beam–column moment-resisting connections using glued-in rods (GiRod) and compares the results with model predictions. Three connection geometries and varying numbers of rods and member size were tested and compared. This experiment will be helpful in grounding research by bringing in new experimental results and proposing an innovative experimentation method. Experimental results showed the high efficiency of glued-in rod connections to transfer loads and bending moment between spruce pine glulam timber members. The observed limit states of the connections were failed steel rods in ductile tensile yielding or wood splitting around the anchorage installed perpendicularly to the grain in the column. It was found that the tested connections behaved as a semirigid moment-resisting connection and exhibited a ductile failure mode when wood splitting was avoided by design. Comparison of experimental results with model predictions showed good agreement, with a deviation under 15% for the moment capacity of the connection.

The North American construction industry has seen substantial growth in the use of cold-formed steel (CFS) framing for midrise buildings in recent years. In seismic zones, CFS-framed buildings utilize shear walls to provide the primary lateral resistance to earthquake induced loads. Although oriented strand board (OSB) and plywood panels have been traditionally used as the sheathing material for these essential components, more recently, steel sheet sheathing has emerged as a novel strategy due to its strength, ductility, ease of installation, and use of noncombustible material, among other benefits. To address the paucity of data regarding CFS-framed shear wall response within actual wall lines of buildings, a two-phased experimental effort was conducted. Wall-line assemblies were fabricated and tested with shear walls placed in-line with gravity walls. The shear walls chord stud packs include tie-rod assemblies consistent with multi-story detailing. Specimens were either unfinished or finished, and the shear walls were laid out in a symmetrical or unsymmetrical fashion within in the wall line. In addition, both Type I and Type II shear wall and anchorage detailing were investigated. In this paper, the impact of test variables governing the structural detailing of CFS-framed walls are quantified through dynamic and quasi-static tests, and a companion paper presents findings regarding the impact of architectural variations on seismic performance.

Although cold-formed steel (CFS) framing systems have the potential to support the need for resilient housing, the use of CFS has been restricted due to gaps in understanding its structural behavior and by the limited guidelines provided in design standards. In particular, the contribution from nondesignated lateral systems and portions of the building system not specifically designated by the design engineers has not been substantially investigated through experiments. To address these shortcomings, a two-phased experimental effort was undertaken to assess the impact of gravity walls, finish application, window openings, and their relationship with the designated lateral force–resisting system. The wall-line assemblies tested, which have shear walls placed in-line with gravity walls, adopted chord stud packs with a tie-rod assembly and were either unfinished or finished, and laid out in a symmetrical or unsymmetrical fashion. In addition, both Type I and Type II shear wall and anchorage detailing were investigated. In this paper, the impact of test variables governing the nonstructural detailing of CFS-framed walls has been quantified, and a companion paper presents findings regarding the impact of structural detailing.

This study was aimed to conduct a thorough experimental investigation on the seismic performance of semiconfined unreinforced brick masonry (SC-URBM) building as a structural topology. Experiments were conducted on two identical full-scale single-story brick masonry buildings: one is completely unreinforced (URBM), and the other is retrofitted with semiconfining horizontal and vertical reinforced concrete (RC) elements (SC-URBM). Both buildings were subjected to FEMA 461 specified reverse slow-cyclic quasi-static loading protocol to quantify the improved seismic performance of the SC-URBM building compared to the URBM building. From the experimental results, ductility capacity, load carrying capacity, and energy dissipation capacity were evaluated, along with important observations such as failure mechanisms from prepeak to postpeak regimes. The results and observation from the experiments demonstrate that the semiconfining elements significantly enhance the energy dissipation capacity and ductility of the retrofitted SC-URBM building without compromising its strength, thereby implying the superior performance of such buildings in comparison to URBM buildings.

The existing machine learning (ML) models for vibration-based damage assessments often use highly compressed features or are restricted to preprocessed signals with fixed durations and sampling rates. Additionally, the learning capacities of ML models and computational resources are limited, which restricts using raw signals as direct input. This paper studied Mel filter banks (MFBs) for seismic signal processing, inspired by speech recognition technology. It is argued that the same filter designs in audio engineering may not be appropriate for seismic records, and therefore, a customized filter bank formulation was developed. Hybrid deep learning models for rapid assessments (HyDRA) were introduced as multibranch neural network architectures that enable end-to-end training for different types of processed vibration data structures. Moreover, the performance-based earthquake engineering (PBEE) equation was adjusted to integrate ML model uncertainties for probabilistic assessments. The proposed concepts were validated in a case study based on a data set of 32,400 nonlinear time-history analyses of a highway bridge in California. Insights and guidelines are provided for optimum filter design based on 5,184 experiments. Several HyDRA architectures were compared with benchmark models. The optimized MFB feature type outperformed features obtained from continuous wavelet transform and a stacked vector of conventional earthquake engineering indexes. A Bayesian variant of HyDRA was investigated to showcase its integration in the modified PBEE equation. Adopting custom filter banks with the HyDRA architecture enables effective feature extraction from raw vibration records by diversifying feature space and preserving information in the time and frequency domains.

Peridynamics (PD) has been increasingly used to study the damage behaviors of reinforced concrete (RC) structures due to its strong capacity in analyzing discontinuous problems. In this paper, bond-based peridynamics (BPD) is enhanced for refined analysis of bond-slip behaviors between concrete and ribbed steel rebar in the pullout test. The enhancement of BPD includes the following: (1) an axial-shear interaction (ASI) model for refined simulation of bond-slip behaviors between steel ribbed rebar and concrete; (2) a nonlinear uniaxial concrete model to avoid excessive compression of concrete bonds; (3) a novel gradually weakening fictitious element (GWFE) approach to improve the stability and convergence of the Newton algorithm in solving the PD equations, e.g., in case of negative concrete stiffness; (4) a horizon updating approach for rebuilding bond interactions when large displacements occur in the bond-slip process; and (5) a parallel computing approach to improve the computational efficiency of refined analysis. The enhanced BPD method is implemented in an open-source finite-element software, OpenSees, and verified by a rebar pullout test. The type of steel rebar rib, strength of concrete, cross-area of steel, and cyclic loading condition are investigated in detail regarding their effects on the stress redistribution and mesoscale crack propagation of the RC members. The results demonstrate that the enhanced BPD modeling method presented herein is capable of fine simulation of bond-slip behaviors in the pullout test, e.g., the strength deterioration, stiffness degradation, and cyclic response.

Endplate moment connections with shape memory alloy (SMA) bolts provide self-centering for the seismic resilience of structures. Predicting the self-centering response of these new beam–column connections, which have not been codified yet, requires conducting experimental tests or detailed continuum finite-element simulations. Computationally efficient predictive tools are needed to facilitate the analysis, design, and assessment of self-centering connections and moment frames. In this paper, artificial neural networks (ANNs) are used to develop a MATLAB tool for predicting the moment-rotation backbone and self-centering response of extended endplate connections with SMA bolts. As the input for the neural networks, the predictive model development employs a design database of response parameters from 72 finite-element (FE) models and experimental tests of seven beam–column connection specimens. Neural networks are trained for seven response parameters, and the trained networks are used to develop a graphical user interface (GUI). The coefficient of determination for the trained ANNs is in the range of 0.92 to 0.99, indicating acceptable prediction accuracy. Furthermore, optimization studies using a multiobjective genetic algorithm are performed, seeking the minimization of material use (steel and SMA) and improved connection-response characteristics (i.e., stiffness, strength, and ductility). A phenomenological model of SMA connections is also developed in OpenSees. The use of the ANN-based predictive tool for accurate and efficient modeling of SMA-based connections and self-centering moment-resisting frames is illustrated. The computation time for predicting the moment-rotation response of a typical SMA connection is significantly reduced from seven hours in ANSYS to only three minutes in OpenSees while providing the same level of response prediction accuracy. Furthermore, the optimization results are confirmed by performing nonlinear pushover and response history analyses.

The time-varying mean (TVM) component has a major influence on the characterization of nonstationary wind events and associated parameters of the fluctuating components. However, it is challenging to determine the optimal TVM of the nonstationary wind speed accurately due to variability in the low-frequency signal contents. To address this challenge, this study develops an effective wavelet-based method together with necessary conditions to calculate the optimal TVM from nonstationary wind speed data. For comparison, the time-dependent memory method is also used and enhanced to obtain the optimal TVM. Wind field turbulence characteristics of Typhoon Mangkhut are then analyzed and presented based on the conventional stationary model and nonstationary model with the proposed optimal TVM. In addition, this study also proposes an empirical description of the wind spectrum, which provides a better fit to the typhoon-related nonstationary winds than those offered by classical wind spectral description.

As the tsunami threat across the Pacific coast becomes better understood, vertical evacuation structures are being widely considered in order to improve life safety. The design of such structures requires careful consideration of fluid-induced forces. Recently, core walls have been used as a preferred system for lateral force resistance in tsunami-resistant structures. These structures require high strength and stiffness provided by walls both orthogonal and parallel to the demands; detailing and limiting shear stress demands provide the necessary ductility. There are, however, potential challenges to utilizing core wall systems for tsunami-resisting systems. Primarily, walls orthogonal to flow tend to draw large hydrodynamic and hydrostatic forces during tsunamis. Therefore, accurate estimates of these demands are needed for the design of resilient structures. A four-phase research program utilizing integrated experimental and numerical methods was undertaken to investigate these demands and the efficacy of current design standards in providing reasonable but conservative estimates for the forces imparted. The first phase of the program used computational fluid dynamics (CFD) to simulate the experiments, building on prior research. The second phase used the results from the simulations to define the bathymetry in the flume and the placement of instrumentation. In the third phase, a 1:6 prototypical scale core-wall structure was tested in the large wave flume at the Hinsdale Wave Research Laboratory, a Natural Hazards Engineering Research Infrastructure (NHERI) testing facility. The experimental setup permitted the testing of the full core-wall system, including the pile foundation and rough estimates of the impact of soil restraint on the demand. Strain gauges, load cells, and pressure distributions were used to provide advanced measurements of the structural response. These measurements were then used to validate the modeling approach. The fourth phase involved comparing the measured peak forces from experiments to standard design equations for imparted force against structures due to tsunami inundation using data acquired from the experiments with the intent of investigating tsunami load demand imparted to a structure after an earthquake. Earthquake loads were not taken into account in experimentation or analysis; they simply dictate a building’s capacity against the initial event.

Dynamic simulation of self-centering systems can be computationally challenging due to the opening and closing mechanisms that cause a rapid change in stiffness. In addition, the current modeling of self-centering connections requires several degrees-of-freedom per connection. This paper presents a new element for the analysis of self-centering systems to address this issue. The element formulation includes its self-centering end connections. It relies on an analytical formulation, where the elongation due to openings is considered. Furthermore, to overcome the highly nonlinear behavior of such systems, mainly due to the opening and closing of the self-centering connections, the proposed element relies on an algorithm with multiple linear brunches to define the deformation state. The proposed element can be used with standard time integration schemes with small modifications, where in this paper the well-known Newmark Beta method is adopted. The reliability of the presented element was demonstrated through two numerical examples of a wall with multiple rocking sections and a five-story self-centering moment-resisting frame (SC-MRF). The numerical results show good agreement compared to a finite-element explicit gap model for the self-centering connections, while the proposed element requires a significantly reduced number of nodes and degrees-of-freedom. Therefore, the computational effort required using the proposed element is considerably smaller. This is demonstrated using a five-story SC-MRF example.

The paper presents the results of a comprehensive wind tunnel study dedicated to addressing the effects of the underneath array clearance on wind loading of roof-mounted solar panels. Indeed, the array clearance has a crucial influence in many respects ranging from its consideration in the wind tunnel modeling to its impact on structural safety. A set of atmospheric wind tunnel experiments was carried out on three configurations of a multipanel solar array mounted on a flat roof immersed in a simulated atmospheric flow of open-country exposure. The solar array was placed at three clearance heights above the roof, namely, 0, 20, and 40 cm (in full scale). Wind tunnel measurements of the mean and peak pressures on both bottom and top surfaces of the solar panels as well as of net pressures across the panels were carried out. The results show that the impact of the underneath array clearance on the panel wind-induced pressures depends highly on the wind direction and the location of the panel within the array. Generally, the wind-induced pressures on solar panels when lowering the array clearance become quite severe and may peel off the panels from the supporting racking system; on the other hand, at such clearance installation, the panels are subjected to lower downward net pressure. Furthermore, the study highlights the potential uncertainties in the wind tunnel experimental results that could be deemed as actual design loadings when the underneath clearance is of concern. This has important ramifications on the formulation of design provisions to be used by solar panel professionals.

This paper presents an experimental study on the seismic performance of a three-dimensional (3D) joint between concrete encased steel cross-shaped (CESC) columns and steel beams. Cyclic loading test of five interior joints was performed to investigate failure modes, hysteretic behavior and strain distribution. Steel configuration, load ratio, and loading angle were considered. Seismic performance was evaluated based on peak load, stiffness degradation, energy dissipation, and ductility factor for these joints. The test results indicated that the seismic performance of joints with solid-web steel is much better than that of joints with T- and U-shaped steel trusses. The ultimate drift ratio of all joints was larger than the minimum limit of 1/50 in American and Chinese standards. The strain results showed that the influence of loading angle on the shear capacity of 3D joints cannot be ignored. Ultimately, because of the rhombic coordinate relationship between shear strength and loading angle, the formulas established in this paper can be adopted to assess the shear capacity of 3D joints between CESC columns and steel beams.

The paper proposes an adaptive fiber section discretization scheme for inelastic frame elements. The scheme uses cubature rules for the efficient and accurate evaluation of the section response over the elastic portion of the section. As inelastic strains arise and penetrate into the section from the edges, the scheme converts the area under inelastic strains to a regular fiber discretization. This approach offers considerable advantages for the computational efficiency of large structural models with inelastic frame elements by minimizing the number of integration points in sections with limited inelastic response. The proposed scheme is presented for circular and rectangular cross sections, but the approach is applicable to other section shapes. Inelastic frame response examples demonstrate the benefits of the proposed discretization scheme for the nonlinear response history analysis of large structural models.

Existing web crippling design provisions available in European, American, and Australian/New Zealand standards are based on empiric equations that differ from the approach adopted for the treatment of other instabilities such as local or overall buckling that employs $\chi \text{-}\lambda$ curves. Assessment of those empiric web crippling provisions based on test data available in the literature and reported herein for interior-one-flange (IOF) and interior-two-flange (ITF) loading conditions has demonstrated that they provide unsafe and inconsistent predictions, thereby highlighting the need to develop an alternative approach. Focusing on aluminum tubular sections subjected to IOF and ITF loading conditions, this article reports experimental and numerical results that were used to develop $\chi \text{-}\lambda$ curves for web crippling design. The tubular sections were made of 6060 and 6063-T6 aluminum alloys and were manufactured by extrusion. A total number of 12 tests were carried out and subsequently used to develop and calibrate a numerical model. The measured dimensions, material properties, and web crippling loads attained are reported. After successful calibration of the numerical model, parametric studies covering a wide range of slenderness and support lengths were carried out. In order to derive the $\chi \text{-}\lambda$ approach, three numerical analyses were performed as part of the parametric study: (1) a linear elastic analysis, (2) a plastic analysis, and (3) a geometrical and material nonlinear analysis. A total number of 288 numerical results were used to derive the new method. Compared with European, American, and Australian/New Zealand standards, the derived $\chi \text{-}\lambda$ design method provides more accurate and reliable predictions for the web crippling of aluminum tubular sections.