Practice Periodical on Structural Design and Construction

This research offers an experimental study of the behavior of reactive powder concrete (RPC) deep beams with openings externally bonded by carbon fiber-reinforced polymer (CFRP) strips. The beam specimens are classified into three categories. The first category contains two RPC deep beams without strengthening. The second category has six RPC deep beams strengthened with different schemes of CFRP strips without mechanical anchorage. The last category includes four RPC deep beams strengthened with CFRP strips and using mechanical anchorage (bolts). The results showed that using a CFRP system as an external strengthening technique has an important effect on the overall response of the tested beam specimens. The ultimate strength of the deep beams with openings increased by 11%–94% compared to nonstrengthened specimens.

A building experiences progressive collapse when a primary structural element fails, resulting in the failure of adjoining structural elements, which in turn causes further structural failure. The final failure contains no proportionality to the primary failure. For initial damage, progressive collapse codes and regulations suggest the alternate load path method, which is a threat to independent procedure. However, considering blast loads in analysis is recommended by some researchers. This paper aims to compare various column removal procedures due to blast loads in progressive collapse analysis of reinforced concrete moment-resisting frames. First, the damaged column is identified by analyzing single structural components (columns) under various blast scenarios defined by the quantity of explosive and location of the blast center outside of the structure. To find the damaged columns, three local analyses, static, dynamic, and pressure impulse (P-I), were carried out. A global incremental dynamic analysis of the three-dimensional (3D) damaged structure is the second step of the analysis. This methodology is threat dependent. Therefore, the results are compared to the threat-independent method introduced in guidelines.

Reducing damages to underground utilities is one of the primary goals of construction stakeholders. The societal and economic impacts of such damages are substantial. To minimize potential damages to underground utilities, one-call notification programs have been created to coordinate efforts that aim to locate utilities before excavating. One-call centers are distributed throughout the United States and have been collecting damages data for years. However, few, if any, studies have evaluated the overall process of one-call centers and whether their services are adequately designed and efficiently delivered to utility owners and excavators. Thus, the present study aims to fill this gap in practice by investigating underground utility damages and evaluating the overall process. To achieve the aim of the study, two methods of data collection were adopted. Damage data from the state of North Carolina in 2017 were obtained to examine trends and frequencies of damages. In addition, a survey was developed and used to evaluate the overall process of one-call centers and identify deficiencies. Among other findings, the results suggest that damages to telecommunication and television (Tele/TV) lines are more frequent than other types of damages and that, overall, Tele/TV contractors are the primary contributors to most damages. The study also reveals that locate time is the most deficient component in the locating process. Findings from the present study are expected to help construction stakeholders and state agencies improve the locating process and management of underground utilities.

The principal direction of inertia in the ultimate limit state under axial load and biaxial bending of a doubly symmetrical reinforced concrete section is not the same as the direction of the principal axis of symmetry. If a hyperbolic stress–strain relationship is used to describe the behavior of concrete in compression, then, to some extent, the maximum capacity direction deviates from the apparent main axis of inertia (the main axis of symmetry). This study explores the real maximum capacity direction of bending of two reinforced concrete sections with a variable amount of steel using two different axial compression loads and two different stress–strain relationships for concrete (parabolic-rectangular and hyperbolic). The results are presented in a collection of interaction diagrams.

Current governing codes and standards in the United States provide engineers with an option to design structures for the load effects caused by a fire. This process consists of calculating the required thickness of fire protection material on each structural member due to the actual performance of the structure in a fire event and considering the inherent fire resistance of the structure itself. Although this process may not be necessary for all building types and construction, for some buildings structural fire engineering can result in significant financial, environmental, and performance benefits for the building. The results of this study showed that for buildings with enhanced design objectives, implementing structural fire engineering can result in more economical structures that have an improved fire resistance, shorter schedule of construction, improved safety of the job site, and less global warming potential (GWP) due to the more efficient use of building materials during design.

In recent years, retrofitting and strengthening of steel structures with carbon fiber reinforced polymers (CFRPs) is a rapidly developing technique that has attracted the attention of many researchers. Most previous studies in this area have been carried out on the behavior of straight steel sections. Vertical curved steel beams are typically used in structures, such as steel bridges, steel trusses, and others. Given the presence of an axial force in vertical curved beams, the performance of such beams under vertical loads is different from that of straight beams. To the author’s knowledge, no independent article has studied the effect of CFRP strengthening on the behavior of vertical curved steel beams with a square hollow section (SHS). However, this study explored the effect of CFRP strengthening on the structural behavior of the vertical curved SHS steel beams under concentrated load or uniformly distributed load using finite element investigation. To analyze and study the effects of CFRP strengthening on the behavior of the vertical curved steel beams, three-dimensional modeling and nonlinear static analysis were used. The results indicated that using CFRP to strengthen the vertical curved steel beams in some specific locations has a significant effect on increasing the ultimate capacity of these beams. CFRP strengthening could further increase the ultimate capacity of the vertical curved steel beams under concentrated load over the ultimate capacity of the vertical curved steel beams under uniform distributed load.

Evaluating the state of stress of a cylindrical shell based on elastic analysis originally involved a series of hypotheses concerning the conditions around it and the structural material used. All of these hypotheses involved either idealizing a reality that was impossible to ascertain a priori, or referring to an ideal, homogeneous, and isotopic material, even though RC does not have any of those properties. However, it was impossible to guarantee that the state of stress obtained in the shell represented the indisputable real state of the structure. Due to the progress made in the study of plastic methods, a key figure in this context is Knud Winstrup Johansen; in 1944, he published a pioneering article which set out the origin of the application of limit analysis to the structural calculation of long cylindrical roof shells based on a plastic approach to equilibrium, enabling simple and accurate calculation of these types of structure.

Seismic analysis provisions in ASCE/SEI 7-16 (ASCE. 2016. Minimum design loads and associated criteria for buildings and other structures. ASCE/SEI 7-16. Reston, VA: ASCE.) use an approximate fundamental period as a proxy for, or to limit, the fundamental period of a building for design. This design period does not vary as a function of the risk category assigned to a building. Fifty-four steel buildings (4-, 8-, and 16-story) with three different seismic force-resisting systems (moment frame, concentrically and eccentrically braced frame) are designed for a region of high seismicity for Risk Category II, III, and IV. The results indicate that the analytical fundamental period is affected when an importance factor greater than 1.0 is used for design, as is required for assigned higher risk categories. Moreover, the database of measured vibration data taken from steel buildings used to establish the empirical formula adopted by ASCE/SEI 7-16 to compute the approximate fundamental period did not include buildings designed with an importance factor. Consequently, if the performance objective is to achieve uniform risk within a category, then the design period should vary as a function of the risk category. In the absence of a lower-bound empirical formulation for the approximate period using a database of vibration data from buildings categorized by risk category, a straightforward modification to the current formulation is proposed that incorporates the change in system strength.

The dynamic characteristics of a reinforced concrete box-girder viaduct have been quantified through on-site dynamic testing. The results have been compared with the results of another set of tests carried out on the same bridge, 25 years ago. Both investigations, i.e., the old and the new ones, included ambient vibration testing as well as operational modal analysis. In the modal tests carried out previously, simple equipment utilizing a few uniaxial accelerometers had been employed repeatedly and the natural frequencies of the bridge had been extracted by simple peak-picking technique from the frequency response functions (FRF), while in the modal tests conducted recently more advanced triaxial accelerometers were used in a rather fine measurement grid and the dynamic characteristics of the bridge were determined by means of commonly used frequency domain decomposition (FDD) and enhanced frequency domain decomposition (EFDD) modal identification techniques. The paper highlights the actual dominant modes and the corresponding mode shapes and focuses on the changes in the natural frequencies and damping characteristics of the viaduct after 25 years. Supporting finite-element models of the bridge have been constructed and updated in accordance with the results of the modal tests. Through a parametric study, the effects of changes in influential variables such as the radius of curvature, the material properties of members (time dependent properties of concrete), the effective member sectional properties, and the shear stiffness of the elastomeric bridge bearings have also been investigated. Finally, a discussion has been provided to address the minimum sensor placement for possible permanent monitoring of such a bridge with sufficient accuracy.

Full-depth precast deck panels are commonly used in RC bridges in order to speed their construction. In this study, two configurations of the closure strip between precast slab panels were proposed and filled with either nonshrink grout or ultrahigh-performance strain-hardening cementitious composite (UHP-SHCC) material. The proposed closure strips were strengthened by externally bonded carbon fiber–reinforced polymer (EB-CFRP) sheets in order to compensate for the drawback associated with decreasing the amount of connected steel reinforcing bars required to transfer bending moment between both panels. Twelve specimens divided into three groups were cast and tested under short-term nonreversal repeated patch loads simulating the wheel load at the central joint. Test results revealed that the UHP-SHCC filling material enabled the connected panels to exhibit more ductile behavior compared with panels using nonshrink grout. On the other hand, the CFRP-strengthening sheets for the first configuration of the closure strip failed to allow the CFRP-strengthened connected specimen to restore the ultimate capacity of the unstrengthened monolithic specimen. However, the second configuration of the closure strip using UHP-SHCC filling material enabled the connected panels to restore the lost capacity and outperformed it by about 14% compared with the unstrengthened monolithic specimen.

Risks are an inseparable part of every project, and risk management must be one of the main requirements of every project. According to risk management experts, risk identification and analysis is the most important part of risk management, and can be called the core of risk management. True identification and precise analysis of risks and implementation of risk management in a project can reduce time and cost and improve quality and safety. This research comprehensively and systematically identified and assessed risks in the Iranian bridge construction industry. Risks were identified during various visits and interviews and through questionnaires, risk factors were prioritized according to statistical test results, and quantitative analysis of risks by Monte Carlo simulation was implemented on a real project and its implications on project time and the cost were determined. Financial risk was the most crucial risk factor which negatively influenced projects. Practical solutions for risk assessment and analysis of bridge construction projects are offered which can be utilized by contractors, project managers, and project control engineers in bridge construction companies.

Construction operations such as hydrodemolition, diamond grinding, and grooving of concrete infrastructure generate large amounts of concrete residuals. These residuals can be slurry water with suspended or dissolved concrete solids, relatively large solid pieces of concrete, and wastewater, which must be disposed of or beneficially reused. In many instances, these residuals are classified as inert debris, allowing them to be reused as soil amendment or as fill material instead of disposed of in a landfill or a municipal wastewater treatment facility. Guidelines and regulations regarding the disposal and handling of concrete residuals differ in every state. This paper provides an overview of the current state of the practice in the United States in the disposal and reuse of concrete residuals, with an emphasis on identifying differences in state transportation agency requirements and currently utilized and potential methods for recycling these residuals.

Much of the construction literature that examines safety culture and safety climate ignores the unique characteristics of construction workplaces. Therefore, existing safety culture and climate models do not capture the true nature of construction practices where the upper management, such as project managers and safety coordinators, often manage several construction projects. Accordingly, a framework that addresses the contribution of the management personnel as well as the site-level personnel has been presented as part of the current research. The proposed framework captures safety culture and safety climate using the following two distinct factors: (1) the management safety (MS) factor and (2) the site safety (SS) factor. A survey was administered to collect the perceptions of construction practitioners and site personnel regarding the suggested variables of the MS and SS factors. In addition, the experience modification rate (EMR) was collected to assess the relation between the suggested model and the overall safety performance. The results obtained provide support for the proposed model by suggesting that the MS factor significantly influences the SS factor and that the two factors are negatively associated with the EMRs of the participating organizations. Furthermore, the findings suggest that the MS factor represents the construction safety culture and the SS represents the construction safety climate.

In this paper, the effects of air tightness tests on steel box structures with rectangular or circular cross sections typical of port cranes (legs, arms, and crosspieces) are analyzed. Legs and arms are generally made with elements with profiles having a square or rectangular cross section, while the diagonal struts are made with profiles having circular cross sections. To verify the air tightness of these elements, a necessary requirement to protect them from corrosion if they are not protected with other protection techniques, air tightness tests are performed. These tests, in the framework of durability tests, must be carried out while maintaining the structure elasticity well below the yield limit of the material. The tests must therefore be carefully designed regarding the choice of the air pressure to be injected into the box structures to verify their tightness and the way the air is put into the structures. As shown in the present work by means of an experimental investigation supported by numerical analyses, the choice of the test pressure depends on the shape of the element to be tested and in particular on the shape of the cross section of the profile. To this end, by means of laboratory tests on small-scale models and numerical simulations in the nonlinear field, the actual induced stress state of the internal pressure on the watertight box structures is shown, indicating the values of the pressures, which produce local yields or ruptures.

This paper discusses the ultimate capacities of bolted gusset plates that fail by tensile rupture. In addition to the block shear failure mode to which most gusset plates in bridge trusses and those in braced building frames are subject, a narrow tapered gusset plate may also fail in the inclined net section fracture mode. The inclined net section fracture mode has been observed in failed gusset plates, but to the authors’ knowledge no explicit formula has been proposed in the literature for use in engineering practice. This paper first demonstrates that, for a rectangular bolted gusset plate failing in net section fracture, the ultimate capacity can be determined accurately using the net section across the whole width, without any reference to the Whitmore concept. It then shows through finite-element analysis that the outer net section fractures of a tapered plate are inclined rather than normal to the loading direction. A practical design equation is proposed to determine the net section tension capacity of a tapered gusset plate, and is shown to reasonably match the ultimate loads of specimens tested by independent workers. The existing resistance factor can be applied conservatively to the design equation. This paper includes examples illustrating the governing failure modes of rectangular and tapered bolted gusset plates in tension.

Tuned mass dampers (TMDs) are one of the strategies implemented in the field of structural vibration control. Most researchers have only focused on the control of one specific mode of vibration by idealizing the structure as a single-degree-of-freedom system. From a practical point of view, the use of a single large TMD within a structure would adversely affect the architectural appeal, usable space, and ease of installation. This study introduces a multiple tuned mass damper (MTMD) system, which is simple and more effective than a conventional single TMD system. The system consists of multiple smaller dampers distributed within the structure either uniformly, varying linearly, or based on the judgment of the designer. TMDs tuned to the first, second, and third natural frequencies are used to control vibrations, thus enabling a wider bandwidth of vibration control and attaining remarkable reductions in floor displacements, floor accelerations, and base shear. A MTMD system was investigated for different base excitations, namely harmonic and seismic. A three-degrees-of-freedom frame model and three mass dampers tuned to all three natural frequencies of the system were fabricated. This building model was studied experimentally and analyzed to investigate the effect of harmonic base excitation on structures. Compared with single TMD systems, the performance of the proposed MTMDs system was found to be excellent in controlling displacements. A five-degrees-of-freedom structure was analyzed for seismic excitation to study the effect of two mass dampers tuned to first two natural frequencies with a mass ratio of 5%. The proposed system significantly reduced the displacement, acceleration, and base shear response at the next-higher-order natural frequency beyond the fundamental. The responses of the structures were compared to assess the optimal placement of dampers to attain highest performance. Vibration control by multiple TMDs was found to be more efficient when dampers are strategically placed on the floors, with the maximum amplitude in the mode shapes corresponding to the respective tuning frequencies.

Built between 1973 and 1977 and first opened in 1981, the Rande Bridge was at the time of its completion one of the largest cable-stayed bridges in the world. By 2006, the bridge had reached its maximum capacity and either an expansion or a replacement was needed. Following thorough studies, an expansion in the form of two additional girders, located on either side of the existing deck, was finally selected. Although the foundations needed no retrofitting, the existing towers and anchor piers required some work to accommodate the new girders and their stay anchorages. A careful execution and a detailed construction sequence have allowed a fast erection pace while maintaining the traffic at all times, a requirement needed due to the great importance of the motorway running over the bridge for the area. The successful completion of the Rande Bridge expansion, the first of its kind and size in cable-stayed bridges, has revealed new possibilities to adapt existing major bridges to an increased traffic demand by adding extra traffic lanes.

The design and construction of four 15.3-m-deep neighboring basements in the Hongqiao Central Business District (CBD) in Shanghai, China, were made challenging by the mega excavation sizes ($\mathrm{135,491}{\mathrm{m}}^2$) and the presence of pre-existing utility tunnels nearby. To safeguard the project, save project costs, and reduce construction duration, innovative design and construction solutions were implemented, which included composite earth supporting systems, comprehensive ground treatments, zoned construction methods, special soil removal and disposal procedures, and long-term field monitoring. Benefiting from these composite design and construction solutions, the existing utility tunnels underwent very limited lateral displacement, and their maximum settlements were just one third of the magnitudes estimated before construction. Several key findings were obtained: (1) zoned construction methods, combining zoned soil-removal and strut-casting procedures, proved to be cost effective for the concurrent excavation of mega basement groups; (2) by avoiding side-by-side excavation, adverse superimposing effects deriving from concurrent excavations were remarkably mitigated; (3) the left-in-place earth supporting structures for construction of utility tunnels helped restrain lateral tunnel displacement; and (4) if the soft subgrade below utility tunnels had been improved prior to the adjacent excavations, tunnel settlements could have been reduced significantly. The optimum treatment depth for the soft subgrade below utility tunnels should extend below the elevation at which the maximum lateral displacement of the adjacent multipropped retaining wall occurred.

Tension control (TC) bolts are the most-used bolt in steel building construction. They are designed to be tightened using a TC gun. It is not unusual to find places where the TC gun will not fit. In this case a torque wrench should not be used, because torque settings for TC bolts do not, or more specifically should not, exist. The simplest, and preferred method, is the turn-of-nut method. Once snug tight, a further ⅓ turn for short bolts or ½ turn for longer bolts is all that is required.