Journal of Structural Engineering

Stresses in structural steel members of steel-framed buildings during construction are difficult to predict with certainty using conventional engineering methods. In order to inform current design practices and provide information to partially evaluate if a steel member can be reused after its service life, construction-induced strains in a typical building were recorded. Specifically, two columns and three Beams of a four-story steel-framed building were instrumented prior to delivery to the construction site using a wireless sensor network. Data were recorded for 48 days, while the structure was erected and the concrete deck poured, up to fireproofing the building. The data were analyzed considering dead load force effects during various construction phases, impacts, and temperatures. The analysis revealed high variations in temperature throughout the structure and consequently significant temperature-induced stresses as well as greater magnitudes of flexural stress in columns than expected. As a result, the recorded stresses differed by 1–120 MPa (0–18 ksi) compared to the theoretically predicted stresses. Yet, the maximum measured stress [160 MPa (23.2 ksi)] was only 46% of the nominal yield strength. Measured stresses were also used to calculate member forces, and the combined member forces resulted in a maximum of 55% of the yield limit. Thus, the results validated current design practices and the possibility of reusing structural steel.

Postearthquake reconnaissance and recent research on seismic risk analysis have shown that nonductile concrete frame structures are much more susceptible to collapse than modern code-conforming frames. The performance-based assessment paradigm has been a persistent research theme over the last decade within the earthquake engineering community in order to estimate seismic fragilities and earthquake loss for these nonductile concrete frames. This paper proposes a nonlinear performance-based methodology to evaluate different retrofit methods considering hazard level, target performance levels, and life-cycle cost estimates. The structural performance is the main parameter considered for the optimization, although a life-cycle cost analysis is also presented. As a case study, the longitudinal frame of an existing building was modeled considering the effect of flexural-shear-axial load interaction in order to capture column shear and axial failures. The presented performance-based procedure identifies the most economic retrofit solution that satisfies structural response requirements for a given performance level.

A considerable amount of research studies have demonstrated the capability of metallic sandwich panels in dissipating blast loading energy. Metallic sandwich panels dissipate blast energy through large plastic deformation of the core and plates, making them more effective than a single metallic plate of similar density. This study numerically evaluated the effectiveness of using woven shapes as a new core topology in sandwich panels for resisting blast loads. The results of the proposed woven shapes were compared to honeycomb and folded shapes to examine their effectiveness in blast mitigation. Numerical models were developed using ANSYS Autodyn software and were validated using available data in the literature. Eleven panels were studied: three honeycomb panels, five folded panels, and three woven panels. The effect of changing the front layer’s thickness and the back layer’s thickness was investigated. A new scenario was investigated where the same sandwich panels were exposed to a second blast load following the first one. Finally, the effect of changing the charge weight was studied where parameter charts for the honeycomb topology, folded topology, and woven topology were developed. The results show that woven shapes achieved the best energy dissipation capability compared to the honeycomb and folded shapes. Moreover, woven shapes achieved less back layer deflection than the folded shapes and more back layer deflection than the honeycomb shapes.

Steel special moment frames (SMFs) with built-up box columns are often used in taller buildings when two orthogonal axes of participating moment frames intersect. Interior diaphragm (or continuity) plates are usually required to strengthen the column at the beam flanges. A common US practice is to use the electroslag weld (ESW) process to provide complete-joint-penetration (CJP) groove welds connecting the plates to the blindside of the box column after it has been welded closed. Available research in Asia has shown that ESW joints used in this application are vulnerable to brittle fracture. Limited research and guidelines are available in US seismic design codes. The design standard for prequalified connections is primarily developed for SMF connections with wide-flange columns in strong-axis bending. To address the use of large box columns in SMFs with reduced beam section (RBS) connections, a test program with three full-scale specimens was conducted; the depth of the column section also exceeded the prequalification limit. Test results showed that the quality of ESW and SMF joint detailing was crucial for the integrity of the connections. Modifications to ESW detailing and welding process included the use of beveled containment plates intended to delay crack development that might initiate from a notch-like condition inside the flange of the box column. SMF detailing recommendations include an enlarged weld access hole geometry and steel backing treatment of the beam top flange.

The study dealt with rigorous finite-element analysis of wood-frame houses to study the influence of the roof, side and partition walls, and base connection (of wall to lower structure, such as a concrete foundation and a wood floor system) on the in-plane load resistance of the walls. Detailed finite-element models of wood-frame houses were developed by incorporating all the connection details. Simulation results of a complete house and a standalone wall of a full house were validated against responses from the literature. Based on the simulated responses, it was demonstrated that the in-plane load resistance of a wall is significantly underestimated when the resistances are evaluated from a standalone wall considering no system effects from the roof and side and partition walls. Hence, a system effect factor is proposed as a function of wall aspect ratio and presence of roof to take into account the increase in in-plane load resistances of the walls calculated based on the available analytical methods. The results of the analysis also demonstrate the effect of the connection between the wall frame and the lower structure. When the wall frame is connected to the lower structure with nails instead of anchor bolts, the walls of the house tend to overturn rather than undergo shear deflection of the oriented strand board panels, resulting in lower in-plane load resistances. Therefore, based on the simulated responses, a reduction factor is proposed for the in-plane load resistance of the wall when the wall is connected to the lower structure with nails.

The use of high-strength steels for tubular structures has been forbidden or permitted with some joint-strength reduction in most representative international standards. Six rectangular hollow section (RHS) X-joint specimens were tested under axial compression to investigate inelastic joint behavior. The key test parameters included brace-to-chord width ratio and grade of steels. All high-strength steel specimens exhibited sufficient strength compared with current European standards’ strength criteria; their strengths were even higher than the standard’s prescribed unreduced nominal strength. Significantly different postyielding behavior was observed depending upon the brace-to-chord width ratio and the grade of steels. It was also observed that the formulation of sidewall buckling strength in the current European standard tends to predict overly conservative results and requires further examination. A new design formula for RHS X-joints subjected to sidewall buckling was proposed in this paper based on a more realistic buckling shape. When the normalized plate slenderness ratio newly defined in this study is used in conjunction with the column curve $c$ of the European standard, both accuracy and consistency of strength predictions were significantly improved compared with those of the strength formulas currently available.

Cross-laminated timber (CLT) is gaining popularity in residential and nonresidential applications in the European and North American construction markets. For the adequate design of CLT shear walls, quantification of their lateral resistance is of paramount importance. In this paper, investigations with respect to the resistance of CLT shear walls for platform-type buildings under lateral loading are presented. Based on the possible kinematic motions of CLT shear walls under lateral loading (rocking or combined rocking and sliding), formulas were proposed to estimate the in-plane resistance for both single and coupled walls. Five different wall configurations were considered: (1) single walls with brackets only; (2) single walls with brackets and hold-downs; (3) coupled walls with brackets only; (4) coupled walls with brackets and 2-hold-downs; and (5) coupled walls with brackets and 4-hold-downs. A comparison of the proposed formulas against test results of single and coupled CLT shear walls is presented. With further validation, the proposed formulas to estimate the resistance of CLT shear walls could become a useful tool for engineers in the future design of CLT platform buildings.

This paper investigates the behavior of octagonal high-strength steel tubular cross sections under axial compression. Experimental investigations were conducted on cross sections with three nominal dimensions fabricated from different routes of welding or combinations of cold-bending and welding. Material properties and geometric imperfections of the cross sections were measured and are reported here. A total of 18 stub column tests were carried out; load-deformation histories and failure modes of octagonal high-strength steel tubular-section stub columns are presented and discussed. Nonlinear finite-element models were validated to replicate the stub column tests and subsequently applied to carry out parametric studies for further investigating the structural performance of octagonal tubular cross sections with various slenderness values under axial compression. The results from experiments and finite-element modeling are used to evaluate the applicability of codified cross-section classification limits and various existing design methods to octagonal high-strength steel tubular cross sections under axial compression. Modifications to the cross-section classification limits and design methods are proposed to obtain more accurate predictions of cross-section classification and strengths of structures for efficient structural design.

The rotational flexibility of column base connections is commonly assumed to be detrimental to the seismic response of steel moment-resisting frames (MRFs) because it increases story drift demands and promotes soft-story formation by lowering the point of inflection, thereby exacerbating the moment demand at the first-story column top end. However, recent experimental research indicates that wide-flange steel columns with flexible boundary conditions may have enhanced response because base connection flexibility delays the plastic hinge formation and local buckling progression within the column cross section near the base. Local buckling greatly reduces the lateral and torsional restraint at the column ends such that the delay in local buckling also delays member instabilities, which often control the deformation capacity of wide-flange steel columns. This effect was examined parametrically through 2,160 continuum finite-element (CFE) simulations validated against physical experiments. Parameters examined include the applied axial load ratio, the column length, and the lateral loading protocol for the column sections, along with five levels of column base connection flexibility. The results indicate that base connection flexibility has a significant (and positive) influence on key aspects of column response, including (1) lateral deformation capacity, which is on average 40%–50% greater for a realistic value of flexibility, relative to a fixed-base condition; and (2) residual column axial shortening, which is important from the standpoint of retrofit and reparability (a 30%–60% decrease). These benefits are more pronounced in cyclic (versus monotonic) loading histories and for members with cross sections more prone to out-of-plane instability. The implications of these findings are outlined for existing buildings as well as prospective design methodologies. Limitations are discussed.

The continuous hybrid fire-simulation method proposed in this paper is a robust method that allows numerical models with a certain level of complexity to be used in a real-time hybrid fire simulation. Extrapolation and interpolation are used for continuously generating displacement commands during the simulation. The elastic deformation of the loading frame is compensated for during the continuous command generation. The stability issues relating to the stiffness of the loading system and the proposed error-compensation scheme are discussed in depth. A large-scale hybrid fire simulation was carried out to validate the proposed method. A steel moment-resisting frame with reduced beam section connections was selected for the validation test. One column of the selected structure was physically represented in the lab, and the rest of the structure was modeled numerically. The physical specimen was heated with a standard fire curve, with the temperature in the numerical model increasing following the numerical heat-transfer analysis result. A multiresolution numerical model was used as the numerical substructure. The test results confirmed the proposed method can accurately simulate the behavior of a structure subjected to high temperature and subsequent failure.

Despite the remarkable longevity of heritage constructions, they typically present several structural fragilities inherent to their own material and constructive features. This fact is particularly relevant when seismic loads are concerned, because a very significant portion of such constructions lack adequate seismic resistance and require retrofitting interventions in order to mitigate their vulnerability. However, to guarantee the success of the interventions, the interventions should be carefully selected based on a full understanding of the dynamic response of the building and, particularly, its most vulnerable structural elements. Due to many reasons, the issues associated with this kind of analysis are still difficult to address; therefore, research on this subject should be encouraged. Taking this into account, the church of Santa Maria de Belém, one of the most emblematic buildings of the monastery of Jerónimos complex in Lisbon, is used in this work as a case study to discuss the nonlinear dynamic response of cultural heritage buildings. The nonlinear dynamic behavior of the church was numerically simulated with a three-dimensional (3D) model using artificially generated seismic acceleration time histories, in agreement with seismic hazard scenarios for return periods of 475, 975, and 5,000 years. The dynamic response of the church is discussed and a comparison against results derived from a pushover analysis is also presented. Finally, a modal analysis is presented, estimating the damage level that would be present in the church after the occurrence of such seismic scenarios.

High-strength steel is gaining more attention from engineers due to its high strength-to-weight ratio and cost effectiveness. However, the research on cold-formed high-strength steel (CFHSS) tubular members subjected to combined compression and bending is limited. This paper, therefore, presents an experimental investigation on this combined loading scenario, in particular at the cross-section level. The test specimens consisted of five square hollow section sizes and two rectangular hollow section sizes. The nominal proof stresses of the test specimens were between 700 and 900 MPa. A total of 51 short beam-columns were tested to investigate the behavior of CFHSS rectangular and square hollow sections subjected to combined compression and bending. A set of different initial loading eccentricities were adopted to attain a wide range of bending-to-compression ratios. The compression and bending capacities, load-deformation histories, and failure modes of the test specimens were reported. Based on the test results, the design methods described in American, Australian, and European codes were evaluated. Finite-element modeling methodology for CFHSS tubular beam-columns is also presented.

The use of smart dampers in civil engineering structures for vibration attenuation has proven to be promising in recent years. Nevertheless, evaluating the effectiveness of smart dampers in multiple-degree-of-freedom (MDOF) dynamic systems is a time-consuming task. This hurdle hinders the consideration of potential families of controllers for a reliable design and tuning process. Consequently, the current study develops a probabilistic approach by introducing a new theory of semiactive control gains to enable the solution of highly nonlinear control systems with smart dampers by employing the Lyapunov function. The primary objective is to test a hypothesis that the tuning of controlled semiactive dampers in MDOF systems can be performed analytically without the burden of numerical simulations. As opposed to current simulation methods, the proposed probabilistic approach can be used to significantly reduce computational efforts. Accordingly, the proposed approach is useful for the design and evaluation of the efficacy of smart dampers in MDOF systems, such as multistory buildings and wind turbines. In addition, the developed control theory will enable the use of accelerated performance-based semiactive controller tuning, with a potential to advance innovative technologies for building smart, resilient, and sustainable structures that can survive multiple hazards.

Most steel moment frames rely on beam yielding to safely handle the inelastic drifts that will be imposed by severe earthquakes. More resilient steel moment frame concepts such as post-tensioned self-centering frames and friction connections have not seen widespread use, perhaps because they deviate dramatically from current practice. Experimental work was performed to investigate the performance of a new moment frame connection called the replaceable shear fuse connection. The replaceable shear fuse connection uses beam flange plates with special cutouts to prevent beam damage. Seven reduced-scale specimens were tested to investigate the effect of fuse geometry on drift capacity, connection strength, and connection stiffness. The specimens achieved maximum drifts of 0.06–0.10 rad without experiencing strength degradation prior to fuse tearing. The shear fuses experienced strain hardening of 1.39–1.75 times yield, similar to high strain hardening that has been observed in shear link testing. The connections had more-than-adequate stiffness to be classified as fully rigid. Full-scale testing should be conducted to evaluate the effects of beam depth, column depth, and fuse parameters.

The 2010–2011 Canterbury Earthquakes in New Zealand highlighted the vulnerability of gravity load resisting reinforced concrete frames in older buildings that do not comply with modern building design standards. Three full-scale reinforced concrete beam-column-joint frame subassemblies, representative of 1980s construction in New Zealand, were constructed and tested to failure to assess the deformation capacity of the subassemblies. The subassemblies differed in the spacing of joint reinforcement and surface roughening at the ends of the precast beams framing into the joint. The circular columns were nominally identical in all tests and were compression-controlled with a transverse reinforcement ratio of 0.0006 and a ratio of spiral reinforcement spacing to an effective depth ($s/d$) of 0.74. The columns were susceptible to flexure-shear failure. Column failure occurred in all tests, with the failure plane propagating along a diagonal crack for two of the three tests. The lateral drifts at the column axial failure were 2.39% and 3.03% for the two columns that failed along a diagonal crack and 4.85% for the column that did not fail along a diagonal crack. It was demonstrated that the difference in performance can be attributed to variability in concrete strength, which is shown to have a significant influence on the likelihood of flexure-shear failure of the columns.

A dual-fused H-frame (DFHF) is an efficient structural system that combines damped H-frame (DHF) modules with welded wide flange fuses (WWFFs) to create a structural solution that is efficient in construction and more seismically resilient. Each DHF module consists of two columns pin connected to a beam with two buckling restrained knee braces (BRKBs). Each DHF module can be prefabricated at the factory, shipped to the site, and connected vertically using simple bolt connections. The connections between the DHF modules have relatively small moment demand, which makes the design, fabrication, and construction of the DHF modules very efficient. Once the DHF modules are assembled vertically, the bays of the DHF can be connected using WWFFs. WWFFs are simple shear connectors that can stably dissipate earthquake energy. In this paper, two prototype DFHF buildings of varying heights (three and nine stories) are designed using the equivalent energy design procedure (EEDP). The EEDP is a novel design method that was developed to design innovative systems, where the structural system can satisfy different performance objectives under different earthquake shaking intensities. To verify the performance of the DFHF, advanced finite-element models are developed using OpenSees and subjected to an extensive array of time history analyses. The results show that the proposed EEDP designed DFHF can meet the targeted performance objectives under different seismic shaking intensities. In addition, DFHF has a sufficient margin of safety against collapse. Hence, the proposed DFHF can be used as an efficient structural system in high seismic zones.

Out-of-plane failure of masonry walls is often responsible for the partial collapse of unreinforced masonry structures. Modeling the out-of-plane response of these walls is therefore key in the assessment of existing buildings. The paper presents a new trilinear model describing the force-displacement response of vertically spanning unreinforced masonry walls subjected to out-of-plane loading. Different factors that affect the response of the walls are captured by the model: the support conditions, the level of applied axial load, the slenderness ratio, and the deformability of the wall. The model is validated against experimental results from shake table tests. The force and displacement parameters of the model are described by analytical expressions that are derived from a mechanical model previously developed for unreinforced masonry. They offer an alternative to existing trilinear models in which corner displacements are mainly defined by empirical relationships.

In order to solve difficulties in the construction of composite steel-reinforced concrete structures, the rebar cage is replaced with steel fiber to form a steel and steel fiber–reinforced concrete (SSFRC) structure. Pushout tests of 20 square specimens were carried out to study the load transfer mechanism in SSFRC, and load-slip curves were obtained. The failures of all specimens were divided into four modes. The bonding stress transfer mechanism on the interface was analyzed thoroughly, and as a result, full-stage load transfer on bond slip could be divided into five stages and five limit states. Values for three bonding forces (chemical bond, mechanical bite, and friction) were calculated. Measured bond stress was highly consistent with that derived from the theoretical full-stage analysis. When loading was relatively high, bond stress increased with it but the increment between each stage was smaller. Further, when loading was close to ultimate, this increment experienced a major drop or even negative growth in the area near the free end. The flange of the H-shape steel provided greater maximum bond stress and greater overall bond force than the web under loading.

The base-isolation system is increasingly adopted for tall buildings for which the wind-induced response is of concern. Previous studies have shown that the wind-induced response can be reduced as compared to a fixed-base building when the hysteretic damping generated by yielding of base-isolation system is noticeable. The yielding also causes the responses of the base-isolation system and structure to have non-Gaussian probability distributions. This study examines the accuracy and effectiveness of statistical linearization approaches for estimating stochastic inelastic crosswind response of base-isolated tall buildings via comparison with response-history analysis for a wide range of structural parameters. The hysteretic base-restoring force is represented in a Bouc-Wen model in terms of hysteretic displacement, base displacement, and velocity. The linearization is to represent the hysteretic velocity as a linear function of hysteretic displacement, base displacement, and velocity. Both Gaussian and non-Gaussian statistical linearization approaches are investigated, where these responses are assumed to follow Gaussian or non-Gaussian probability distributions. To capture the higher-mode contribution to building acceleration, the building motion state variables are also included in the linearization of hysteretic velocity. The results show that the Gaussian linearization approach is able to give quite accurate estimations of building top displacement and base shear force in a wide range of wind speeds or ductility factors of base displacement. However, it underestimates the base displacement and building top acceleration at higher wind speeds. Consideration of a non-Gaussian distribution of hysteretic displacement and inclusion of additional building-motion state variables in the linearization lead to much improved estimation of building acceleration. A further consideration of the non-Gaussian distribution of base velocity results in improved estimation of base displacement.

In this research a seismic retrofit system consisting of a pin-jointed steel frame and rotational friction dampers is developed for the seismic retrofit of reinforced concrete soft-first-story structures, and its efficiency is evaluated through theoretical formulation, cyclic loading test, and analysis of a case study structure. In this system, pin-jointed steel frames are attached to a framed structure at the first story, and a rotational friction damper is installed at each corner of the steel frames. A theoretical formulation is derived for the amplification mechanism of the rotational friction damper and is used to design the geometry of the damper in such a way that its rotation is maximized for a given lateral drift of the structure. The experimental and analysis results show that the proposed system can be used efficiently to prevent the collapse of the case study structure and reduce interstory drift ratios to the code-stipulated limit states.

An important element of time-dependent reliability analysis of civil structures is choosing a proper model for the applied loads. Stochastic process theory has been widely used in existing studies to perform structural time-dependent reliability analysis. However, the use of many types of power spectral density functions leads to an inefficient calculation of structural reliability. This paper proposes an analytical method for structural reliability assessment, where a new power spectral density function is developed to enable the reliability analysis to be conducted with a simple and efficient formula. A non-Gaussian load process, if present, is first converted into an equivalent Gaussian process to improve the assessment accuracy. Illustrative examples are presented to demonstrate the applicability of the proposed method. Results show that a greater autocorrelation in the load process leads to a smaller failure probability. The structural reliability may be significantly overestimated if one simply treats the non-Gaussian load process as a Gaussian one. Moreover, the impact of modeling the load process as a continuous process or a discrete one on structural reliability is also investigated.

Designers favor laminated glass due to its inherent robustness. However, there is disparity between the various design codes currently available for laminated glass and the methods therein for calculating resistance to lateral-torsional buckling. This study examines the effective thickness methods found in some existing codes, which calculate the degree of composite action achieved by a laminated glass section subject to in-plane loading. These design methods are compared using relevant accompanying methods from the standards to calculate buckling loads and glass strength where appropriate to gain an understanding of how these methods are implemented in the industry. Results from the calculations are compared to published experimental data in order to assess the relative accuracy and range of applicability of each method. A parametric study is also undertaken, using results from a numerical model to predict the lateral-torsional buckling capacity of laminated glass sections with various geometries and properties. A significant range in results from the various design methods has been observed. It has also been found that some design methods give consistently nonconservative results.