Journal of Structural Engineering

Pendulum tuned mass dampers (PTMDs) are one of the most commonly used devices for high-rise structures to control large-amplitude vibrations due to dynamic excitations. In practice, the damper of PTMD usually connects the tuned mass to the location below the top floor rather than to the top floor, which is different from the case using a conventional tuned mass damper (TMD). Therefore, the classical optimal parametric formulas derived from the structure-conventional TMD model are not applicable to design the optimal parameters of PTMDs. In this paper, the simplified mechanical model of the structure-PTMD system is updated to consider the damper connection in practice. The fixed-points theory is employed to analytically derive the optimum design formulas for the PTMD by introducing the effect of modal shape. Moreover, the control effectiveness of the PTMD using the proposed method is studied. The control performance and robustness of the PTMD designed by the proposed method are compared to those designed by the classical optimum formulas under various dynamic loads. Finally, with the help of the performance degradation index (PDI), the control performance degradation of PTMD designed by classical formulas is quantified. The results show that the proposed optimal parameters have considerable differences from classical formulas. Through designing a PTMD on a multi-degree-of-freedom (MDOF) structure, the proposed optimum design is demonstrated to be more effective and robust than the classical formulas. To design a large mass ratio PTMD, the control performance degradation from the damper connection in practice is significant and should be seriously considered.

This paper investigates the behavior of eccentrically loaded connections made by combining fillet welds and high-strength pretensioned bolts. New models are introduced for characterizing the load-deformation behavior of slip-resistant bolted connections with different faying surface conditions. These models are utilized to improve the ability of the instantaneous center of rotation (ICR) method to predict the capacity of eccentrically loaded connections utilizing friction as a load-transfer mechanism including bolted-only and/or bolted-welded combination connections. Experimental results are used to quantify the accuracy of the ICR method in predicting the capacity of these combination connections considering different connecting elements to be participating in a single load resisting system. Finite-element (FE) analysis is used to investigate the load-transfer mechanisms within the combination connections. Reliability analysis is conducted using FE analysis assisted by machine learning to quantify the reliability level of the investigated connections and establish the resistance factors necessary to maintain the reliability level above prescribed thresholds. The reliability analysis shows that using the ICR method for designing these combination connections leads to a highly reliable connection for different types of faying surfaces.

The 2010–2011 Canterbury earthquake sequence highlighted the vulnerability of New Zealand light-frame wood buildings that are the predominant typology in residential construction. While life-safety performance was excellent, many buildings experienced widespread cracking of internal wall linings that resulted in costly repairs and disruption. Despite the widespread use of light-frame wood construction in New Zealand, no known shake table tests have been documented for this construction typology. Additionally, New Zealand light-frame wood building performance cannot simply be inferred from international testing because New Zealand adopts a different design philosophy from those of the US and Canada by relying on gypsum sheathing as the primary lateral resisting element. To further investigate New Zealand light-frame wood building performance, this paper discusses shake table testing of a light-frame wood building specimen, constructed on the University of Canterbury unidirectional shake table using modern New Zealand design and construction approaches. The observed damages during the tests were consistent with those observed in similarly built structures that were investigated after the 2010–2011 Canterbury earthquake sequence. This paper also presents a modeling approach using the state-of-the-art software Timber3D, which was verified by simulating the shake table specimen and comparing the observed and predicted dynamic response from the test specimen and model, respectively. The Timber3D modeling approach included analysis and parameterization of screw-slip data using the Evolutionary Parameter Hysteretic Model, formulation of two-dimensional wall component models, and nonlinear time history analysis of a three-dimensional model of the shake table specimen. The model was shown to reasonably predict the displacement response of the shake table specimen and the strength degradation from cracking damage through repeated earthquakes. The modeling approach described is intended to further the development of residential building models toward the performance-based seismic design of light-frame wood buildings in New Zealand.

Abstract

Steel side-plate connections are reliable load path alternatives because they eliminate the fabrication challenges associated with continuity plates, especially for concrete-filled tubes (CFTs). In this paper, a new easy-to-fabricate moment connection for connecting I-beams to CFT columns using the monolithic side-plate technique is proposed. In this connection, the vertical side plates are entirely replaced by column webs to save steel material by eliminating the use of double steel plates in the connection panel zone and resolving the biaxial fabrication issues associated with the lack of welding access between the orthogonal side plates and the column. Four full-scale experimental tests consisting of two couples of relatively identical bolted and welded connections were conducted under a cyclic lateral displacement control loading protocol and a constant compressive axial load was applied to the column to evaluate the seismic performance of the connection. Furthermore, standard geometrical limitations, such as the column width and beam depth, were challenged. The results indicated that the new proposed connection exhibits sufficient stiffness and high level of ductility up to more than 4% of story drift without any strength degradation, implying that this new connection can be classified as a prequalified rigid moment connection to be used in special moment frames (SMFs) located in high seismic regions.

Practical Applications

In this paper, a monolithic side-plate connection is proposed and four full-scale specimens with oversized geometrical characteristics are experimentally investigated. The favorable results of this study show that this connection can be used as a prequalified rigid beam-to-column moment connection in intermediate and special steel moment frames consisting of box columns. The proposed easy-to-implement connection offers advantages such as decreased weight, fewer welding operations, and biaxial connection capability, which are not possible with conventional side plates. This connection is successfully implemented in an IMAX multicomplex building, with $\mathrm{151,676}{\mathrm{m}}^2$ gross area and 82.32 m height. The proposed idea is applicable to any project with large box-shaped columns in high seismic regions and the achievements of this study can provide experimental support for the seismic design of these buildings. Critical factors in the connection performance are the column width and side-plate geometry, and considering other specific aspects of this connection, there is a lot of potential for further numerical and experimental investigations. Although not shown in this work, the proposed approach gives us the necessary flexibility to easily develop a biaxial moment connection, and further research is recommended in this case.

This paper presents the experimental results of two welded unreinforced flange-welded web (WUF-W) beam-to-column connections that defy the current design paradigm of prequalified welded connections. The proposed WUF-W connections feature customized beveled backing bars that are intentionally left in place after the completion of the beam flange-to-column face complete joint penetration welds. The connection design aims at a stable hysteretic response by exploiting the beneficial aspects of appreciable panel zone shear yielding (i.e., inelastic shear distortions of at least $15{\gamma }_y$, where ${\gamma }_y$ is the panel zone shear distortion at yield), by considering a shear strength-to-demand ratio of 0.8. To prevent divot fracture in the column, minimum through-thickness toughness requirements were imposed for the steel column material. The experimental results suggest that the proposed WUF-W connections achieve a stable hysteretic response up until lateral drift demands of at least 7% rad, while a non-softening response was assured up to 9% rad. The beveled backing bars minimize the associated fracture potential near the beam web centerline, which is a primary concern in prequalified field welded moment connections when conventional weld backing bars are employed. The tests suggest that, under a symmetric cyclic loading protocol, local buckling near the steel beams is prevented up until a lateral drift demand of 6% rad, which is an important finding from structural repairability and stability standpoints. The ultimate failure modes of the welded connections, which are attributable to ductile crack initiation and propagation, are consistent regardless of the employed lateral loading histories, which involved standard symmetric cyclic and collapse-consistent loading protocols. The implications for the seismic design of steel moment resisting frames (MRFs) and the limitations of the present work are discussed.

Concrete-filled U-shaped steel beams can be alternatives to conventional composite beams with I-section steel. In this study, a novel U-shaped composite beam is proposed, with a bolt assembly of two Z-shaped steel and a bottom plate. Focusing on the negative flexural behavior of bolted U-shaped composite beams, two experimental programs were carried out: (1) monotonic negative bending on six beam-to-girder connections (or continuous beams); and (2) cyclic positive and negative bending on two beam-to-column connections. In the specimen design, the degrees of composite action were considered for both headed stud anchors in the slab and bolts in the bottom section. The proposed bolt assembly was expected to provide fully and partially composite actions for positive and negative moment, respectively. The test results showed that the flexural mechanism of the bolted U-shaped composite beams occurred typically with local buckling of the bottom plate and the bottom flanges of the Z-shaped steel. The positive and negative flexural strengths of the proposed composite beams were evaluated based on AISC design practice, addressing the degrees of composite action and the plate local buckling. The structural performance of the test specimens was further evaluated with respect to the flexural stiffness and deflection. On the basis of the test results, design considerations for the bolted U-shaped composite beams were recommended.

Abstract

In response to the increasing need for sustainable construction materials, numerous innovative timber-based structural systems have been developed in the past two decades. While timber-based shear-walls are popular, moment-resisting timber frames have received less attention in recent studies. However, with the availability of ductile and resilient beam-column joints (BCJs), timber frames can now be effectively used either independently or in combination with others. This study explores the feasibility of a dual system, consisting of cross-laminated timber (CLT) balloon shear-wall and glulam moment-resisting frame (CLTW-GMRF), and investigates the potential interaction between the two systems under seismic loading. The building features ductile and energy-dissipative BCJs and hold-downs. A seismic design procedure, based on a targeted moment proportion (MP) between the two systems, is presented and applied on a 10-story building. The building is assumed to be located in Vancouver, Canada, and its seismic performance is examined using 30 ground motion records in OpenSees. The system’s efficiency with respect to engineering demand parameters is studied under different wall-to-frame MP values (50%–50% and 60%–40%) and ductility-related modification factors (2, 3, and 4). The study also investigates the system’s performance with two BCJs and hold-down alternatives with bilinear hysteretic and self-centering energy-dissipative responses. Given the availability of resilient connections, the result highlights that the CLTW-GMRF coupled system is a viable alternative for high-rise hybrid timber construction. Moreover, the system’s performance has significantly improved by using self-centering energy-dissipative systems.

Practical Applications

This paper unveils an innovative design approach and practical application for a CLTW-GMRF dual system. This innovative system incorporates energy-dissipative components that are designed and tested in existing literature: (1) the utilization of replaceable steel damper BCJs and buckling-restrained brace hold-downs, providing high ductility with large energy-dissipative capacity; and (2) the employment of hybrid BCJs made up of post-tensioned tendons and mild steel dissipators, along with hybrid brace hold-downs made up of pretensioned tendons and friction surfaces, which reduce residual deformations following seismic events. Utilizing these systems, the research introduces a versatile seismic design method congruent with existing codes and design standards, while offering flexibility through adjustable wall-to-frame moment proportions. The research also underlines the need for careful consideration of the interaction within the timber wall-frame systems. The implications are substantial amidst the growing trend of high-rise timber construction, aiming to fully exploit the potential of CLT and Glulam frames. Moreover, the research has the potential to serve as an essential resource for engineers aiming to optimize the sustainability and resilience of timber structures, particularly in seismic-prone regions.

Abstract

Since the 1800s, there have been live load surveys and analyses carried out, particularly of area-dependent loads in office buildings. While some occupancies have received careful examination, there has been no systematic review and consideration of reliability-based scenarios for office gathering space live loads. The results of the research reported here indicates (supports) a more consistent, reliable, and economic design load for office gathering spaces in buildings. These results provide the theoretical and practical basis for design live loads for gathering spaces within offices, a step toward possible enactment in the current standard, and subsequently by adoption into the International Building Code and materials standards. Following a review of historical load surveys and theoretical models, the paper presents models and observations of crowding, serving as a basis for a different approach for such areas, including a Delphi among leading design firms in the United States. The paper concludes with recommendations for a new live load use category for gathering spaces for offices.

Practical Applications

Modern office usage often contains work spaces for meeting, gathering, and collaboration. The current standard for minimum design loads and associated criteria for buildings and other structures does not directly address this situation. Interpretation has led to conflicting requirements for the design loads of such spaces, including the possibility of assigning them as assembly areas. This can lead to overdesign and uneconomical structures. This research reviews historical office surveys with an emphasis on assembly spaces, presents the results of a Delphi of design firms throughout the United States, and contains a stochastic maximum load analysis. These various assessments lead to a consistent evaluation of plausible loads for such spaces, and a recommendation for a new subcategory in the standard live load table. The study recommends treating these spaces similar to general offices, with a basic live load of $2.39\mathrm{kN}/{\mathrm{m}}^2$ (50 psf), and permissible live load reduction as is currently in the standard for offices. Exception is made for such work spaces that are directly accessible from outside and intended for use by the general public.

Industry interest in mass timber hybrid construction is driving research into new connections, lateral load-resistance systems, seismic design, and fire safety design for low-carbon structures. However, only limited attention has hitherto been paid to the vibration serviceability of mass timber floor systems, which often controls their allowable maximum floor spans. This study investigated the vibration characteristics and serviceability performance of a promising modular prefabricated cross-laminated timber (CLT)–steel composite flooring solution under normal walking actions through both experimental testing and subjective evaluations. The study demonstrates that the flooring solution is a high-frequency floor system. The floor exhibits transient vibration response and can achieve acceptable vibration performance in residential and office settings. Its vibration performance can be reasonably assessed through the measured vibration dose value (VDV) over peak and root-mean-squared acceleration values when its modules are connected using self-tapping screws. The research outcomes will contribute to the vibration serviceability assessment of CLT-steel hybrid floor systems.

The U-shaped steel-concrete composite beam (USCB) has the superiority of good stiffness, high load-bearing capacity, and good fire performance. In this paper, the numerical simulation and theoretical derivation were conducted for the thermal transfer and fire-resistant research of USCBs. Four fire tests on USCB specimens under the current standard temperature rising curve were used to validate the fire design method. The temperature field models and fire-resistance models were set up to research heat-transfer and structural mechanisms, and the analysis showed that the fire condition of different concrete sections was different in the USCBs, and the internal force redistribution happened in the composite beam. Then, the parametric analysis shows that the load ratio, the diameter of fire-resistance reinforcement, and the thickness of the fire protection layer have significant effects on the fire performance. The temperature calculation methods of U-shaped steel, different concrete sections, and fire-resistant reinforcement are proposed based on the conducted research. Moreover, a flexural bearing capacity calculation method for the USCB under the standard temperature rise curve is proposed allowing for the influence of material strength reduction under high temperatures, which can also be used to calculate the fire resistance. Finally, the calculation tables for the fire protection layer thickness and the corresponding design method are proposed based on the delaying temperature mechanism.

The thread-anchored blind bolt (TBB) is anchored by a threaded bolt hole instead of a nut. It can only be mounted from one side, providing an alternative method to build the square hollow section column connection (SHSCC). A study on the change of mechanical behavior of a structural component after exposure to fire is the key to its reuse or repair after a fire. The tensile performance of TBB bolted SHSCC after a fire, and the effect of the internal strengthening component (ISC) was studied by experiments. The full-period method was adopted in the test to consider the influence of the load and temperature on the postfire behavior of the TBB bolted SHSCC. Two failure modes of the TBB bolted SHSCC were observed in the test, and the column wall thickness decided the failure mode. Increased load or temperature could cause the connection to fail previously in a fire but not change the failure mode. The TBB bolted SHSCC could recover most of its resistance after cooling down. Comparative tests were also conducted to assess the difference between the SHSCC bolted by TBB and standard bolt (SB). TBB and SB connections with the same configuration showed the same failure mode under the same condition. The TBB and SB connections demonstrated similar postfire performance when the column wall thickness was large. However, the SB connections showed a much better safety reserve than TBB ones when the column wall thickness was limited. The ISC improved the performance of TBB bolted SHSCC significantly when the column wall thickness was limited. The TBB bolted SHSCC strengthened by ISC could also be comparable to the TBB bolted ones.

Abstract

Origami-based structures have been widely implemented in the design of deployable systems. They possess desirable properties such as easiness in manufacturing, high transportability, programmability, and the capability to fold into complex three-dimensional (3D) structures starting from planar configurations. However, their geometric complexity poses major challenges in developing efficient design methods, in which optimizing their geometries and folding motions remains a challenging task. This paper investigates the motion and shape inverse design of a Miura-based origami deployable system for architectural applications. The proposed structure folds from a flat to different 3D shapes, has 1 degree of freedom, and can fold rigidly being also flat foldable. The capabilities of the structure to fold approximating symmetrical target shapes of different geometries and achieve tailored folding motions are investigated. Furthermore, an inverse computational design workflow is proposed. The structure showed good accuracy in approximating target shapes, folding within desired motion envelopes, and avoiding collisions with surrounding objects. The origami-based system could be designed to deploy in different scenarios at the architectural scale, and could find applications as deployable canopy for improving comfort in outdoor conditions. Although limited to early design stages, the proposed design workflow is a flexible tool that could be applied to shape and motion inverse design tasks by simply variating its objective function. The method could be further applied to different typologies of rigid-foldable origami-based structures at different scales.

Practical Applications

Current studies on origami-based deployable systems mainly cover geometries that can be deployed, function as static systems, and further folded after the end of their operation. Despite possessing desirable characteristics, such designs fail to take advantage of origami properties such as programmability and dynamic adaptability to different scenarios. In addition, the optimization of such structures and the conception of efficient design workflows remain challenging. This paper proposes a design that could be folded and unfolded dynamically adapting to its environment. Furthermore, a computational design workflow for the design of shape and motion is presented. The novel aspects of the study can be summarized as follows: (1) tailored design of complex 3D geometries using two-dimensional (2D) origami patterns, (2) design of both shape and motion, which extends the common only-shape design approach, (3) development of an efficient and flexible computational design workflow that could be adapted to diverse inverse design tasks with different objectives, and (4) development of the workflow in the Grasshopper interface, in which environmental simulations could be carried out. Thermal comfort, wind comfort, and acoustics are some of the topics of interest that could be evaluated without making any change in the proposed parameterization and optimization framework.

Strong thunderstorm winds cause damage to structures. However, the available number of the tricomponent thunderstorm wind record with a subsecond sampling time interval is limited. In the present study, a record-based procedure for generating tricomponent nonstationary non-Gaussian thunderstorm wind records was proposed. The procedure was based on the iterative power and amplitude correction algorithm framework but with modifications. The modifications were aimed at increasing the variability of the sampled record components by randomizing the power spectral density functions of processes through a digital filter in the frequency domain and improving the convergence by using a relaxation factor for the synchronized phase shift. The formulation and algorithm for the proposed procedure were given by considering the continuous wavelet transform with the harmonic wavelet and generalized Morse wavelet, and the generalized S-transform, which can provide good time localized resolution at high frequencies (low scales) and good resolution at low frequencies (high scales) simultaneously. The proposed procedure, unlike some of the algorithms available in the literature, matches the marginal mixture cumulative distributions of the seed record components and does not require the separation of low- and high-frequency wind components. The use of the proposed procedure to sample tricomponent thunderstorm wind records was shown.

Development of competent composite beam systems has been fostered by the steel industry for structural efficiency. Current flexural design methods were developed primarily for conventional composite systems using a wide-flange section. Posed configuration is characterized by angle shear connectors welded to U-shaped cold-formed steel beams. For verification of code compliance, this study performed 12 composite beam flexural tests. Test parameters considered angle shear connector direction, spacing, and concrete strength. Based on experimental and analytical results, flexural strength prediction by international standards as well as an angle anchor design equation were evaluated. Ensuing thoughts and discussion pertain to the effects of neutral axis depth and partial composite behavior. Findings were deemed beneficial in development of design methods for the posed system. To develop design methods for the posed system, a simplified flexural response analysis model, which relies on just shear connector strength without an exact interfacial shear-slip relationship information, is proposed.

Much of the current code provisions for designing slab-column connections against punching shear are based on empirically derived formulations based on tests of partial scale isolated slab-column specimens. Although many experiments have been conducted on shear reinforced concrete flat slabs supported on columns, due to cost or time constraints, there are still many parameters that have not been adequately studied in the laboratory. These tests can be supplemented by analytical results of properly calibrated nonlinear finite element analysis (NLFEA) to enhance the existing experimental database and formulate rational design recommendations for future codes. This paper presents a rational approach for calibrating an NLFEA model in ABAQUS using interior and edge slab-column connection specimens. The calibration includes a study to determine how to effectively model the shear reinforcement and shear reinforced area. This further includes a detailed analysis of the modeling of the shear reinforcing elements to ensure appropriate rotational capability of the shear reinforced region of the slab without significantly reducing the predicted capacity of the model. The calibrated models show good agreement with test data based on load-deflection, moment-curvature, and bolt strain behavior.

This study aims to assess the effect of notches and holes on the structural performance of laminated veneer lumber (LVL) joists using experimental and numerical methods. A total of 40 samples were manufactured with three different notch depths and without notch and tested under a three-point bending load. Subsequently, detailed numerical models were developed and validated with experimental results. The effect of a notch, hole, and location on the load-carrying capacity, shear and flexural stress, and flexural stiffness of the LVL joist were evaluated through the validated numerical model. Results showed that the hole and notch significantly affect the structural performance of the LVL joist. Further, the notch or hole in the middle of the bending span induces a higher load-carrying capacity reduction (i.e., more than 50%) than that of from shear span. Further, the larger hole (i.e., size beyond 33% of the joist’ depth) located in the shear and bending span reduced the load-carrying capacity by more than 15% and 50%, respectively. A similar reduction was also observed in the flexural and shear stress of the LVL joist. Moreover, this study proposed a response surface-based model to predict the failure load and flexural stiffness of LVL joists with and without holes and notches.

Tornado fatality rates in the southeastern United States are higher than those in Tornado Alley, despite Tornado Alley having a higher frequency of tornadoes. A major contributing factor is the large number of mobile and manufactured homes (MMHs) in the southeastern states. Forensic engineering assessments of tornado damage have consistently shown that inadequate anchoring of MMHs or the absence of proper anchoring has been the primary cause of structural failure. To properly design a MMH anchorage system to resist tornadic winds, it is imperative to have accurate knowledge of the tornadic wind effects on the MMH systems. In this study, tornado–MMH interactions are investigated using high-fidelity numerical simulations. The pressure distribution on the MMH surface and the total forces/moments on the entire MMH induced by tornadic winds are obtained. In addition, simulations are conducted to reveal (1) the difference in tornadic wind effects between a MMH and its associated permanent home (home with classical on-site construction), and (2) the difference in wind effects between tornadic winds and the equivalent straight-line winds. The latter of these comparisons is intended to provide information on the unconservative use of straight-line wind loading for MMHs. The simulation results (peak wind pressure and total forces/moments on the MMH) are compared between the tornadic wind field and straight-line wind field. The comparison indicates that the results caused by the tornado are higher. Under a tornadic wind field, compared with the permanent home (PH), the peak pressure and horizontal forces on the MMH are smaller because of the existence of open space under the MMH. Although the research findings here demonstrate the limitation of US code for MMHs, a great number of simulation cases with the related uncertainties involved will be needed to be run to improve the US code.

Steel plate shear walls (SPSWs) often need to accommodate rectangular openings in their infill plates. When subjected to lateral loadings, such as wind and earthquake, unstiffened SPSWs with rectangular openings may experience large deformations around the openings. This paper presents a stiffener layout to limit the deformations around the rectangular openings in the SPSW system. The effectiveness of the proposed stiffener layout is investigated by conducting experimental tests on two one-third-scale single-story SPSWs with rectangular openings at the center of the infill plates. The two specimens have the same aspect ratio but have different rectangular opening sizes. To prevent deformations around the rectangular openings, the infill plates of the two test specimens are stiffened with the proposed stiffener layout. Quasi-static cyclic loading tests are performed on the specimens, and the deformations around the openings are measured at different loading stages. Tests showed that the proposed stiffener layout can successfully restrain the deformations around the rectangular openings. The specimens also showed stable hysteresis curves and good energy-dissipation capacity. To further examine the inelastic performance of the proposed stiffener layout, finite-element analysis of stiffened SPSWs is conducted. Seismic analyses are also performed for 4-story stiffened and unstiffened SPSWs with rectangular openings to investigate the seismic response of SPSWs with the proposed stiffener layout around the openings. Seismic analyses showed that the proposed stiffener layout around the rectangular openings can prevent the out-of-plane and in-plane deformations around the openings in the SPSW system.

The reinforcing steel bars embedded in the concrete of a reinforced concrete (RC) structure in a region with high airborne chloride concentrations may corrode. To avoid overestimating the seismic capacity assessment, it is necessary to understand the residual shear strength of an RC frame with infilled wall and localized corrosion. This work investigates the residual shear strength of an RC frame with infilled wall and localized corrosion by designing five wall specimens with corroded reinforcing steel bars to obtain the residual shear strength of each RC frame with infilled wall with different corrosion zones. Additionally, a model based on the softened strut-and-tie model is proposed to determine the residual shear strength of an RC frame with infilled wall and localized corrosion. The experimental and calculation results are compared to verify the application of the proposed model for the shear strength of an RC frame infilled corroded RC wall.

The North American Standard (NAS) and the European Standard (EC3) for cold-formed steel design provide limited guidelines for the strength predictions of built-up columns. The existing design equations are limited to flexural buckling and local-flexural interactive buckling. The present study evaluates the local-flexural interactive design equations for cold-formed steel built-up back-to-back I-section columns against the results of experimental and numerical studies. The results show that the existing design guidelines for local-flexural interactive buckling are unconservative by about 17%, 5%, and 15% for DSM-NAS, EWM-NAS, and EWM-EC3, respectively. Furthermore, a maximum reduction in the built-up column strength by local-flexural interaction is observed when its nominal local and flexural buckling loads are close. Based on the results and observations, new design equations are proposed by including the product of nominal local and flexural buckling loads for the North American and European standards, which capture the local-flexural interactive buckling in built-up I-section columns. The effect of fastener spacing on the ultimate load for local-flexural interactive buckling is also evaluated, and its effect is found to be small, unlike for global buckling. The minimum fastener spacing criteria of NAS are assessed, and suitable recommendations are provided for fixed-end columns. Overall, the present study provides insights into the local-flexural interactive buckling behavior of built-up I-section columns and proposes reliable design equations to predict the ultimate load.

The brittle behavior traditional directly welded connections of steel beams to concrete-filled steel tube columns is caused primarily by excessive out-of-plane deformation of the tube walls at the level of the beam tension flange. To address this issue, this study proposes a reference connection that involves fillet welding a built-up steel beam directly to the corner of a diamond-shaped concrete-filled steel tube (DCFST) column. Two options are suggested for enhancing the seismic performance of the reference connection: a predrilled hole with a 12-mm diameter at the midwidth of each beam flange, or a rib stiffener reinforcement on the outside of each beam flange. The two proposed specimens and a traditional directly welded connection were subassembled and investigated experimentally. The results showed that the reference DCFST connection significantly improved the seismic response of the directly welded connection in terms of initial stiffness, strength, ductility, and energy-dissipating capacity. Specifically, the initial stiffness and strength capacity increased by over 150% compared with that of the traditional connection counterpart. Furthermore, the rib stiffeners contributed to further enhancement of the seismic response by shifting the beam plastic hinge away from the column face. Overall, these findings suggest that the use of DCFST connections is reliable for composite moment-resisting frames (C-MRFs), and the proposed enhancements can improve the seismic performance of these connections significantly.

Up to date, few studies on the dynamic characteristics analysis and model updating of large-size ultrahigh-voltage (UHV) transmission towers with long cross arms have been conducted due to the lack of onsite measurement data. In this paper, a framework for vibration test–based dynamic characteristics analysis and model updating of UHV transmission towers is proposed using a fast Bayesian fast Fourier transform (FFT) method with an interactive optimization approach. The dynamic response of a T-shaped $\pm 800\text{-}\mathrm{kV}$ UHV transmission tower is achieved by performing an ambient vibration test. The dynamic characteristic parameters (frequencies, damping ratios, and mode shapes) of the structure are obtained by using the fast Bayesian FFT method. Meanwhile, the relevant uncertainty of the identified parameters is also quantified. Then, an interactive optimization approach is presented to update the model using a set of automatic model correction schemes based on the particle swarm optimization algorithm. The interactive optimization approach is implemented by the continuous iteration process between the software MATLAB and ANSYS. The proposed interacting pattern could be well applied to the model updating of the transmission towers. This study could provide a reference for the field test, structural design, and safety evaluation of UHV transmission towers.

The vulnerability of posttensioned (PT) slabs to fire has prompted researchers to conduct tests and devise means for numerical analysis. In this study, bonded PT slabs with varying cover thicknesses were subjected to fire tests with a numerical model developed based on the results. The test results demonstrate that current codes governing cover thickness adequately address fire resistance. The structural behavior of PT slabs was analyzed based on thermal responses for concrete and steel. Numerical modeling of heat transfer and coupled thermomechanical analyses was validated by comparison with fire test results. To investigate the influence of cover thickness on fire resistance performance, a parametric study to develop a numerical means of analysis was conducted and evaluated. With a load level of up to 40% of nominal flexural capacity at the specified cover thickness of 45 mm or larger, current codes were proven to be adequate to ensure the target safety. The authors hope that identified influencing factors of fire resistance performance of PT slabs and the proposed numerical modeling method may be helpful in design of bonded PT concrete slabs with unrestrained conditions.

As additive construction technologies evolve, the US Army Engineer Research and Development Center has studied the functionality and structural integrity of structures produced using additive construction methodologies. Compared with precast construction, additive construction has multiple advantages including unique geometries, reduction of worker power, no required formwork, and ability to use locally sourced materials. The purpose of this study is to evaluate additively-constructed concrete structures and compare it with conventional construction methods. Static analyses are performed using finite-element modeling on several precast concrete beams and compared with experimental data. A finite-element model was created for additively-constructed beams by incorporating cohesive interaction properties to evaluate the interface strength between three-dimensional (3D) printed layers. To further validate the model, an additively-constructed concrete wall is also experimentally tested and compared with models. Numerical predictions are developed to explore damage caused by interfaces of additively-constructed structures and its effects on the structural performance. Maximum deflections and peak loads were also obtained for the conventional construction method experimentally with finite-element models.

Hurricane and tsunami events can generate extreme water flows in nearshore regions of the United States with catastrophic consequences to coastal structures. Field records have shown that light-frame wood structures exhibit high vulnerability to wave-induced forces due to their light construction characteristics, which feature flexible connections and slender pile foundation systems. Previous research has studied the behavior of these structures under wave action, but most studies used rigid body modeling, which is shown in this study to be insufficient for capturing the force demand on these structures. Using a fluid-structure interaction (FSI) framework, this research investigated the structural and soil flexibility effects in the interaction between elevated light-frame wood structures and water flows. Study variables included the flexibility of timber-to-timber connections, soil type, pile embedment, wavelength, and wave amplitude. The study concluded that structural and soil responses to water flows can introduce strong coupled motions. Neglecting this coupling effect may underestimate the force demand on the light-frame wood structures by more than 40%. Accounting for both structural and soil flexibilities is necessary to accurately quantify the wave force demand of these structures.

Structural applications of hybrid reinforced concrete (HRC) involve a composite system with a fiber-reinforced concrete (FRC) matrix in conjunction with conventional reinforcement. The system offers economic benefits by reducing the number of rebars, minimizing labor costs, and shortening the construction schedule. This paper presents the generalized approach to evaluating closed-form moment–curvature relationships from constitutive models with multilinear equations. The interaction of various moment–curvature solutions is by sequential switching from one mode to the other to form an envelope curve as the minimum moment among all available options. Results lead to explaining the interaction of material and geometrical parameters as well as the interaction of various failure modes. Furthermore, the model can be used for both the ultimate limit state (ULS) and serviceability limit state (SLS) since the strain history is the primary independent variable. These lead to parametric design charts for adjusting material parameters, reinforcement amount and location, and section geometry within the bounds of ${\rho }_{\min }$ and ${\rho }_{\mathrm{bal}}$ is applicable for HRC, RC, and FRC sections. Analytical equations show that as the concrete flexural crack extends in a hybrid section, the bridging effect of fibers delays the stress accumulation into the rebar and its subsequent yielding. The efficiency of the volume of concrete that is under tensile loads is significantly improved, extending the serviceability range and increasing the stiffness of cracked concrete. The extension of the serviceability limit range is also associated with potential improvements in durability since the HRC model predicts smaller apparent strains and crack widths at a given load. The proposed solutions are validated by simulating the load-deflection responses of various full-scale flexural tests published in the literature.

This paper presents a dynamic modal identification of the Fatih Sultan Mehmet (FSM) Bridge utilizing structural health monitoring (SHM) data recorded during a recent extreme wind event (maximum wind speed: $130\mathrm{km}/\mathrm{h}$) that occurred on November 29–30, 2021, to provide a preliminary report for future posthazard health assessments for similar long-span suspension bridges. First, four different operational modal analysis (OMA) techniques are performed to identify the bridge’s modal parameters (modal frequencies, damping ratios, and modal shapes). The analysis results are compared with each estimator and those of an experimental investigation published in the literature to verify the bridge’s modal parameters. Secondly, natural frequency history and damage indicators are determined using the modal parameters and estimated standard deviations obtained from the stochastic subspace identification with extended unweighted principal component (SSI-UPCX) technique. The result of modal damage indicators reveals a healthy structure after this extreme wind event; onsite visual inspections also support this finding. In conclusion, it is believed that these significant findings will lend invaluable knowledge to stakeholders.