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A comparative study of the dynamic behavior of twin single-span bridges was carried out based on operational modal analysis and a linear finite element model updating with the aim of finding a potential damage indicator. The bridges are skewed, 30 m long and with prestressed concrete girders as the main support structure, but one of them were collided and suffered damage in two of its I-shape girders. Ambient vibration tests were conducted by deploying 14 uniaxial accelerometers along the sidewalks, experimental modal parameters were identified using the COVariance-driven Stochastic Subspace Identification method (SSI-COV). Six vertical modes were clearly identified for each structure. Additionally, some extra modes with non-proportional damping were identified. It was found that the modal frequencies are sensitive to the support conditions and the overall stiffness of the bridge but not to the localized girder damage, which, on the contrary, is reflected in the discrepancy in the fundamental bending mode shape amplitude between the lateral sides of the bridge, and a so-called Continuous Symmetry Measure adopted as a symmetry index seems to be a good damage indicator for this type of straight-alignment simply supported bridges, given the symmetric nature of the bending mode shapes and the asymmetric nature of the damage. [ABSTRACT FROM AUTHOR]

Cold-formed steel, prized for its affordability and durability, gains enhanced structural performance through perforated patterns on beams. This study explores the impact of perforation on load-carrying capacity and capability-to-weight ratio in cold-formed steel cantilever beams, specifically focusing on "C" sections. Assessing beams of varying lengths under uniform loading, the investigation, employing ABAQUS software, reveals significant load-carrying capability reductions of 35% to 95% for beams subjected to minor-axis bends, depending on hole quantity and placement. The findings stress the imperative precision needed when incorporating perforated sections into load-bearing structural systems. Flange perforations result in substantial drops, up to 90%, in load-carrying capacity, while web holes in beams bent about the major axis cause only minor reductions. This study informs the establishment of innovative design standards for perforated cold-formed steel beams, enhancing efficiency in construction and minimizing environmental impact. The proposed cold-formed steel cantilever beam exhibits a substantial load-bearing capacity of 185.4 kg/KN, surpassing capacities of simply-supported RC beams (119 kg/KN) and fixed beams (165 kg/KN), suggesting its potential advantages in structural applications. Bridging structural engineering and material science, this research pioneers sustainable and cost-effective construction approaches for the future. [ABSTRACT FROM AUTHOR]

This paper presents a new tub girder series for Colorado, conforming to the articles of the American Association of State Highway and Transportation Officials' AASHTO LRFD Bridge Design Specifications. Although the B618 tub girders developed by the Colorado Department of Transportation in the 1990s have been successfully used for decades, the need for an upgrade is essential to satisfy the requirements of contemporary bridge design and construction. After examining the performance of tub girders selected from six transportation agencies in the United States, an optimization algorithm was employed to generate efficient prototype sections. Then, detailed investigations were conducted to examine various practical aspects concerning the serviceability and ultimate limit states of AASHTO LRFD specifications. Parametric analysis with five bridge superstructures that accommodate up to four traffic lanes demonstrated the applicability of the prototype girders. A simplified version of the prototype sections was also delineated for regional precasters. Furthermore, a comparative study was carried out to evaluate the geometric stability and production costs of the prototype, simplified, and existing B618 girders. [ABSTRACT FROM AUTHOR]

Long precast, prestressed concrete girders are becoming popular in bridge construction. Several states have constructed bridges using slender I-girders that exceeded 200 ft (61 m) in length. When such a girder is seated on flexible supports such as a jeep and dolly, it can roll about an axis located beneath its center of mass. This movement induces lateral bending, which raises concerns about the lateral stability of particularly long girders. While the stability of these girders is largely influenced by the hauling equipment, very few state transportation agencies offer guidelines addressing the rotational stiffness of transport vehicles and other critical parameters. This paper presents comprehensive field measurements of rotational stiffness from various precast concrete plants. It covers two methods--namely, the placement of eccentric loads and the parking of vehicles on a substantial cross slope--to gauge rotational stiffness. The measurements included a variety of transport vehicles with air and leaf suspensions. The examined vehicles displayed a rotational stiffness ranging from 22,000 to 42,000 kip-in. (2486 to 4745 kN-m) per radian. The paper also suggests a guideline for tilt measurements to gather essential data and pinpoint the rotational stiffness. [ABSTRACT FROM AUTHOR]

This paper investigates the failure behavior of reinforced concrete beam - column joints (BCJs) strengthened with different schemes of carbon fiber reinforced polymer (CFRP) and the factors causing fracture. In the study, five reinforced concrete BCJ specimens having 1/1 geometric scale were tested under reversed-cyclic lateral loading. While one of them was used as a reference, the others were strengthened with CFRP. Damage development of the specimens was simultaneously monitored by the acoustic emission (AE) technique. Both the structural and AE data were combined to reveal the effects of CFRP strengthening schemes on the fracture pattern ana damage progress. Quantities, scales, levels, and locations of the damage show that the scale of the damage decreased with all strengthening procedures and that the strength and other mechanical properties improved. In addition, extending the strengthening material to the columns and beams contributed more to the structural behavior in terms of strength, energy dissipation capacity and rigidity as well as crack development. Although strengthening by wrapping only the beam and column extensions of the joint can give the desired performance in terms of load bearing capacity, it is not recommended owing to an increased risk of major shear cracks. [ABSTRACT FROM AUTHOR]

This paper focuses on the shear behavior of reinforced concrete (RC) beams strengthened with carbon–glass-fiber-reinforced polymer (C-GFRP) plates under different anchoring schemes. The study consisted of four reinforced specimens: specimen CS-1 with no reinforcement and three groups of reinforced specimens SR-1, SR-2 and SR-3. The studies used a four-point bending test to evaluate the reinforcement effect of mechanically anchoring C-GFRP plates. The results of the analysis of load–deflection, strain and bearing capacity indicated that a better reinforcement effect was observed with fiber-reinforced polymer. The test results suggested that the occurrence time of critical oblique cracks was delayed and the development speed of critical oblique cracks was limited by mechanically anchoring the C-GFRP plates. C-GFRP plates significantly increased the stiffness of the reinforced specimen and reflected the superiority of mechanical anchoring. The ultimate shear capacity of the mechanically anchored C-GFRP plates has been significantly improved. With a reasonable increase in the amount of C-GFRP plate, the shear resistance of the test beam became stronger. Compared with the CS-1 specimen without reinforcement, the yield load values of the reinforced specimens SR-1, SR-2 and SR-3 increased by 5.56%, 18.80% and 26.50%, respectively. The ultimate load of reinforced specimens SR-1, SR- 2 and SR-3 increased by 11.64%, 17.47% and 31.51%, respectively. The researchers deduced their theoretical calculation method from the bearing capacity of RC beams strengthened by anchoring with carbon–glass-fiber-reinforced polymer plates. The test findings were in good accord with the theoretical calculation model of bearing capacity suggested in this research. [ABSTRACT FROM AUTHOR]

Low-density Zeolite Aggregate (LDZA) is obtained by thermally treated zeolite in a furnace under 500°C. Thus, the water evaporates, and zeolite aggregates (ZA) are obtained with porous structures in which water molecules that make LDZA have endogenous processing properties. In this research, experimental behavior using ZA is used as a replacement portion of fine and Coarse-grained aggregate to obtain Low-density concrete (LDC) beams. The performance of normal reinforced concrete beams was contrasted with that of LDC beams based on their load-deflection behavior, ultimate load capacity, deformation profile, and crack pattern Under the effect of static load. In addition, apertures of different diameters (25, 38,50,60) mm were made in the tensile region along the aperture length of beams to minimize the self-weight of the beams. As a result of the use of zeolite aggregates, there was a decrease in the weight and density of the concrete used in casting the beams, and the results for the Normal Concrete (NC) beam were close to the results from the beam LDC. However, using Apertures in LDC beams in the tensile zone gradually reduced ultimate loads and mid-span deflection. Therefore, it is recommended to use zeolite aggregates to make LDC for use in reinforced concrete elements. [ABSTRACT FROM AUTHOR]

This paper presents finite element simulations of the flexural behavior of three prestressed ultra-high-performance concrete (UHPC) beams based on the concrete damaged plasticity model (CDPM) available within Abaqus. A novel numerical model that applies the prestressing force through surface traction is proposed. The flexural deformation of the prestressed UHPC beams is simulated from the application of the prestressing force through failure under flexural loading. Material properties were measured and informed values for CDPM input parameters. The model was compared with four-point loading tests previously conducted to study the flexural behavior of large-scale prestressed UHPC beams. Digital image correlation (DIC), supplemented with traditional sensors, was used during the test to monitor behavior. The primary results based on the numerical modeling are as follows: * The model is validated to accurately simulate the flexural behavior of prestressed UHPC beams, both in global deflection and local strain. * The prestressing process, including camber deformations, is effectively simulated. * The new approach to apply prestressing force in the model can be applied in scenarios requiring large prestressing forces. * The numerical results are also validated through comparison with DIC results. The new numerical modeling approach will be effective for guiding experimental studies and design of prestressed UHPC beam elements. [ABSTRACT FROM AUTHOR]

Human-induced vibration serviceability often governs the dynamic design of modern footbridges. Many design specifications have been issued, applying different load models, response calculation strategies and comfort limits (three key aspects), which may inevitably cause inconsistent evaluation results for the same structure. It requires the comparison of specifications, and better practical suggestions proposed, to guide the vibration serviceability of footbridges. This article performs the most comprehensive evaluation of specification performance. It includes six current specifications: the UK NA, the HiVoSS guidelines, the Sétra guidelines, the ISO standard, the American guide and the Chinese standard. After comparison of the three key aspects, practical suggestions are proposed. Evaluations are made based on two recent long-span footbridges in China. The footbridges are found to be low in damping ratios and there exist low and close natural frequencies, even closely-spaced modes. Vibration serviceability assessments show obviously inconsistent results owing to differences in the three key aspects. Furthermore, owing to contributions of closely-space modes, the total structural responses are significantly larger than the single dominating mode (often applied in response calculations according to the specifications). Thus, the article suggests considering the contributions of multiple modes in designing for the vibration serviceability of long-span footbridges. Finally, considering large vibrations, mitigation measures are applied. Instead of applying external dampers, e.g. tuned mass dampers (which may add to the economic costs of the structure), effective vibration mitigation measures are suggested by changing structural parameters. Except for the traditionally applied wind-resistant cables, a steel box girder with infilled concrete is applied to the main girder, replacing the original design. As a result, vibration amplitudes are significantly reduced. Footbridges are also made less sensitive to human-induced excitation. [ABSTRACT FROM AUTHOR]

This paper describes an experimental investigation of a novel reinforced concrete buckling-restrained brace for precast concrete lateral load-resisting frame structures in seismic regions. The proposed brace uses ductile reinforcing bars with unbonded lengths across end gaps and bonded lengths at the middle region for lateral stiffness, strength, energy dissipation, and ductility. The experimental program included four isolated diagonal brace subassemblies subjected to reversed-cyclic pseudostatic lateral loading. Local buckling of the energy-dissipation bars across the end gaps is the most critical failure mode that can limit the ductility of the brace in compression. Up to this failure, the bonded and unbonded regions of the braces performed as designed. The results demonstrated the different deformation and stiffness behaviors of the braces in tension and compression. Subsequent loading to large tension displacements provided evidence of the large energy dissipation that can be expected if premature failure of the brace can be prevented. Simplified numerical models provided good predictions of the measured brace behavior until failure. This research featured the first set of tests for this brace, and the results highlighted adjustments needed to design and modeling to achieve the desired behavior of the brace. Recommendations for future research include improved shear dowel and confinement designs to prevent local buckling of the energy-dissipation bars and improved longitudinal reinforcement designs to prevent yielding of the energy-dissipation bars in the middle bonded region of the braces. [ABSTRACT FROM AUTHOR]

The design codes/standards recommend using an over-reinforced beam section for FRP-reinforced structures to use the ductility of concrete to give adequate warning prior to complete failure. In contrast, the present study is based on the nonlinear response prediction of beams prestressed with carbon-fiber-reinforced polymer (CFRP) tendons and designed under-reinforced. The beam is designed here such that a progressive rupture of the CFRP tendons occurs, i.e. they rupture one after the other, introducing a kind of pseudo-ductility, which is enhanced owing to the additional inelastic energy resulting from the sequential rupturing of the tendons. A parametric study has been conducted on CFRP-prestressed concrete beams with different numbers of tendon layers, varying prestressing ratios and several cross sections moreover, a sacrificing warning rebar has been introduced for improving the ductility further. The findings showed that the prestressed concrete beam with multiple layers of CFRP tendons resulted in an improved ductile design as compared to the single-layered system. Additionally, grading of concrete in the beam section has been made to compensate for the reduction in the load-carrying capacity due to the layering of tendons. The pseudo-ductility of such functionally-graded beams has been found to be improved, with energy ratios as high as 78.7% and having comparable load-carrying capacity. [ABSTRACT FROM AUTHOR]

Shear resistance by beams without stirrups presents the transfer of shear and normal principal stresses across the open cracks within reinforced concrete (RC) beams. The complexity of the shear mechanism is further complicated by the distorted structure of RCA, which is composed of hardened adhered surface mortar and virgin aggregate. Compression field theory (CFT) postulates a series of curves for shear-loaded beams to signify the transfer of tensile and compressive stresses in concrete beams across developed shear cracks. Special attention is given to beams with recycled materials, which do not necessarily give the same strength as virgin aggregate. A numerical shear model is developed that accounted for the fracture characteristics, modes I and II of the beam containing RCA along the primary crack path from dowel action, aggregate interlock, and uncracked compression zone of the beam. The model captures the correlation of shear arm ratio, longitudinal reinforcement ratio, maximum coarse aggregate size, and concrete strength. The study model was validated using experimental results from 139 concrete beams containing RCA without stirrups. The strength ratio resulted in mean of 1.32 with a standard deviation of 0.48, a coefficient of variation of 36.8% and R-squared value of 0.65. The statistical evaluations of the model were compared with the other nine (9) theoretical models by authors and codes of practice. The developed model predicted a relatively higher shear strength value due to the inclusion of contribution from dowel action, aggregate interlock and compression zone. [ABSTRACT FROM AUTHOR]

It has been proposed that 0.7 in. (17.8 mm) diameter prestressing strand be permitted for use in bridge girders. If 0.6 in. (15.2 mm) diameter strand is replaced on a one-to-one basis with 0.7 in. strand, the pretensioning force can be increased by 35%. When designs use 0.7 in. strands as well as high concrete strengths, longer-span prestressed concrete girders may be achieved. An extensive analytical study is presented to assess the maximum girder span lengths that can be achieved when using 0.6 and 0.7 in. strands. A parametric design study with 584 cases was conducted to examine the influence of girder shape and size on the potential benefits of using 0.7 in. strands. A detailed finite element analysis of some of the longer spans achieved was also conducted. The impacts of using 0.7 in. strands on end-region detailing requirements, prestress transfer, and handling and erection stability of long-span girders were examined. Girder span increases of up to 22% were achieved using 0.7 in. strand in place of 0.6 in. strand. The larger pretension forces affected end-region detailing and increased congestion, though all resulting requirements were constructible. The longer spans affected girder stability calculations, and some girder types required a wider top flange to meet stability-related limit states. [ABSTRACT FROM AUTHOR]

Deck bulb-tee girders constitute an excellent precast concrete bridge element system for medium- to longspan bridges. The precast concrete girders are transported to the jobsite, where they are placed adjacent to each other. The girders are connected using field-cast longitudinal joints. When required, a continuity diaphragm over the pier is used to create moment continuity; however, there is a risk of cracking of the field-cast joints and construction can be difficult when adjacent girders have different camber profiles. Given these challenges, adoption of the deck bulb-tee girder systems has been limited. Analytical investigation performed in part 1 of this series of papers indicated that using ultra-high-performance concrete (UHPC) can improve the performance of the field-cast joints and help overcome construction difficulties. This paper describes full-scale experimental testing performed as a follow-up to the analytical investigation. Longitudinal joints grouted with UHPC were tested under a combination of thermal and live load. A continuity diaphragm with partial UHPC was also tested under positive and negative moments over the pier. [ABSTRACT FROM AUTHOR]

Seven ultra high-performance concrete (UHPC) beams without shear reinforcement are tested in this work to examine their structural behavior as shear failure is a major concern in such members. Coarse aggregate was not used in two of the beams while the other five are made with coarse aggregate as 50% replacement of fine sand. Three longitudinal steel reinforcement ratios (1.14%, 1.64% and 2.46%) and three steel fiber ratios (0, 1% and 2%) are used. Results show that UHPC beams with coarse aggregate show higher ultimate loads (4.7% − 11.5%) than UHPC beams without coarse aggregate and incorporating 1% and 2% steel fiber raises ultimate loads by 60% and 131%, respectively for beams with coarse aggregate. Also, using 2% steel fiber changes failure mode from brittle shear failure by diagonal crack in beams of 0 or 1% steel fiber to ductile flexural failure by yielding of longitudinal reinforcement. Higher stiffness and toughness and lower deflections are observed with the increase of longitudinal reinforcement, steel fiber or coarse aggregate. Using 2% steel fiber highly improved toughness by more than 17 times. Lower rates of improvement are recorded for longitudinal reinforcement and coarse aggregate. However, it is recommended to perform more research to examine more parameters such as fiber types. [ABSTRACT FROM AUTHOR]

Multi-storey car park buildings with steel–concrete composite floor structures are widespread in construction due to the distinct benefits of the implemented structural system. Although there are various possibilities for accomplishing composite action between a steel beam and a concrete slab, some solutions, such as friction-grip bolts commonly applied in the 1970s, did not show good durability. An example is the multi-storey car park building "Obilićev venac" in Belgrade. This case study presents two methods for life extension of the car park building structure. Both approaches focus on applying welded headed studs with the primary intention of providing a durable shear connection. While the first method has been applied during the structure's reconstruction, the second method is proposed as a novel solution for implementation in steel–concrete composite floors. The application of the proposed connection is discussed and the results of the experimental and numerical research conducted are presented. [ABSTRACT FROM AUTHOR]

Fibers that are used to enhance the residual flexural and tensile strength of fiber reinforced concrete (FRC) are reinforcing materials possessing good mechanical characteristics and properties. The effect of fiber on the flexural strength of FRC at elevated temperatures is limited and hence the present paper studies the influence of fibers (basalt, carbon, glass, polypropylene, polyvinyl alcohol) on strength grades M20, M30, M40 and M50 concrete specimens exposed to elevated temperature for a duration of 30, 60, 90 and 120 min, respectively, with an ISO 834 fire-curve. The objective of the study is to determine the effect of temperature on the flexural strength of fiber reinforced concrete prism and reinforced concrete beam specimens. Past studies have revealed that concrete's tensile strength is one of the primary factors affected by exposure to higher temperatures, more so than its compressive strength. The residual strength of the specimens was determined after cooling in air, and it was found that carbon fiber reinforced concrete specimens retained more residual flexural strength than the other specimens. The residual energy absorption capacity was analyzed and an empirical relationship was established to find the residual flexural strength in terms of the grade of concrete, the type of fiber and the duration of heating. [ABSTRACT FROM AUTHOR]

This paper describes a numerical investigation on the seismic design and behavior of a novel reinforced-concrete buckling-restrained brace component for use in precast concrete lateral-load-resisting frames. The design procedure aimed to develop a brace with ductile behavior under reversed cyclic loading. Nonlinear finite element analyses were conducted to investigate the following potential undesirable failure modes of the brace: global buckling of the brace, closure of the end gaps, and local translational buckling of the energy-dissipation bars. The results indicated that failure through global buckling is unlikely for practical brace designs. Closure of the end gaps can be prevented by designing a wide-enough gap at each end of the brace, but design must also ensure that local buckling of the energy-dissipation bars does not occur over their unsupported length across the end gaps. An axially decoupled steel shear dowel can be used to permit a wider end gap without triggering translational buckling of the energy-dissipation bars. Braces that are designed to prevent undesirable failure modes can provide stable behavior up to ductile low-cycle fatigue fracture of the energy-dissipation bars. [ABSTRACT FROM AUTHOR]

This research studies the flexural behavior of concrete beams reinforced with biaxial geogrids, distributed short glass and steel fibers. No longitudinal steel reinforcement bars were used. Therefore, an amount of short glass and steel fibers was used to improve the concrete beam behavior against flexural failure. Eleven specimens of single reinforced (flexural reinforcement) concrete beams and double reinforced (compression and flexural reinforced) concrete beams using two biaxial geogrids sheet layers, with randomly distributed short glass and steel fibers were cast. The samples were tested using two points of load along the beam specimen span with an increment of loading by 5 KN to evaluate several parameters. The studied parameters are using geogrids as a main flexural reinforcement, using geogrid sheet layers as a flexural and compression reinforcement, using short glass and steel fibers as an additional reinforcement of concrete with various ratios 0.25 %, and 0.75 %. The test results indicated that the use of geogrid layers as the main flexural reinforcement improved the behavior of the concrete beam specimens at failure. As well as; more enhancement of beam specimens at failure was observed when using short glass and steel fibers with geogrid reinforcement in concrete beams. The tested beam specimens which were reinforced by geogrids in the flexural and compression zone using 0.75 % of steel fibers gave better results due to modes of failure, toughness, failure load capacity, crack width, and post cracking stiffness. [ABSTRACT FROM AUTHOR]

Cracks will inevitably occur in concrete structural during the normal use phase due to load action, fatigue effect, and environmental corrosion. Concrete resistance can reflect some internal concrete damage. In this work, three-point bending tests were performed on concrete beams. We simultaneously measured the concrete beam resistance before and after cracking to investigate the feasibility of resistance measurement for achieving self-monitoring of concrete cracking and crack development. This work provides a methodology for the monitoring of engineering structures. It establishes a quantitative reference for the relationship between the number of steel fibers used and their conductive and mechanically sensitive properties. [ABSTRACT FROM AUTHOR]

Deterioration of the end regions of prestressed concrete bridge girders is commonly observed in the field when girders are exposed to chloride-laden water that has leaked through failed expansion joints. Because the deterioration is often localized to the end regions of the girders, reliable repair techniques can provide a means to extend girder service life, avoiding the need for immediate superstructure replacement. To evaluate different repair methods and identify key design considerations for end region repair, shear tests to failure were conducted on prestressed concrete girders extracted from a decommissioned superstructure. Three repair systems were evaluated: an externally bonded fiber-reinforced-polymer (FRP) system, a near-surface-mounted FRP system, and a concrete end block. Only the externally bonded FRP system successfully restored both the strength and initial stiffness of the girder. Although the other two methods were not successful, the tests on the repaired girders highlight important factors that must be considered when designing repairs or conducting further research. The tests also demonstrate that end region deterioration can cause significant (> 40%) reductions in strength, underscoring the importance of addressing such deterioration observed in the field. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

One of the most hazardous consequences of impacts on concrete structures is the high tendency to develop shear or punching failures, with debris generation and associated flying fragments split out. In order to reduce such hazards, concrete structures can be strengthened with a thin bottom layer of high performance fiber-reinforced cement composites (HPFRCCs). As strengthening and anti-spalling layers, the most demanding application is for shear-critical elements, where extensive diagonal cracking leads to multiple fragments, besides concrete cover spalling typical of bending-critical members. An experimental campaign has been carried out on 21 beams to investigate their failure mode. Different configurations were studied for the HPFRCC to determine the influence of the fiber amount (2-4%) and the introduction of embedded steel bars in the strengthening layer. Specimens were subjected to drop weight tests and quasi-static reference tests. The tests have shown that a membrane-type resisting mechanism can be activated by the HPFRCC layer, which can retain potentially falling generated fragments and improve the carrying capacity. Embedding steel bars in the strengthening layers can avoid HPFRCC rupture. Moreover, members strengthened using tensile strain-hardening HPFRCC mixes have shown enhanced strength compared with unstrengthened members, while mixes without strain-hardening did not. [ABSTRACT FROM AUTHOR]

This paper presents a practical optimum design solution of prismatic simply supported prestressed concrete girders that are subjected to uniformly distributed static loads. The process is formulated as a nonlinear optimization model while assuming linear elastic behavior and employing the working stresses method. The process produces the optimum values of two design variables, namely the cross-sectional dimensions and the prestressing force. Those optimized values are computed to satisfy either a minimum weight or a minimum cost objective function. To solve the nonlinear programming models, a program named Nonlinear Programming Prestressed Concrete Optimizer (NLPRECO) was coded in MATLAB® programming environment. Some illustrative design problems were solved using NLPRECO, and their results are demonstrated herein. Sensitivity analysis of the optimized design variables, to variations in design parameters, was also investigated, and the results are presented. Results show substantial improvement over the regular un-optimized solutions and moderate improvement over linear programming optimization solutions. [ABSTRACT FROM AUTHOR]

Pre-stressing concrete is commonly used in construction. One of the challenges that pre-stressing concrete (PC) faces is that fire exposure reduces the strength and serviceability of PC elements, which requires unique design considerations. The pre-stressing strands are more sensitive to high-temperature, deform larger than mild steel, and break quicker. This research investigates the thermal and structural response of totally unbonded pre-stressing T-beams subjected to increased temperatures and continuous service loads. Thermal coating was proposed to avoid damage and load carrying capacity reduction under fire loading. Seven medium-sized post-tensioned concrete beams were tested in a fire exposure (600°C for 3 h) in order to examine the effect of the following variables: presence of thermal coating, the use of different pre-stressing ratios, increasing the concrete cover, and studying the fire effect at the end anchor, which represents the weakest point at the unbonded system. The proposed insulating technique improved pre-stressing beam behavior during fire exposure by improving crack distribution and lowering strength loss. The thermally insulated beam with a high pre-stressing ratio attained 99.3% of the control specimen load carrying capacity, compared to 86% for the unprotected beam. The deflection of the thermally isolated beam was 7.8 mm, compared to 22.7 mm for the unprotected specimen after 180 min of fire exposure. The use of low pre-stressing ratio caused the insulated pre-stressing strands to rapidly deform with low increases in temperature, which caused rapid crack formation. [ABSTRACT FROM AUTHOR]

A finite element (FE) model is carried out to study the bending behavior of concrete beams constructed of high and ultra-high strength concrete (HSC/UHSC) under three-point bending. The simulated beams are reinforced with longitudinal reinforcement bars from fiber reinforced polymer (FRP) material. The ABAQUS FE software is used in the modeling. The FE model was calibrated using the experimental data of the specimens carried out by M.W. Goldston et al. (2017). Twenty-eight validated FE models were performed to study the effects of concrete compressive strength (high and ultra-high), type of FRP longitudinal bars (AFRP, BFRP, CFRP and GFRP), main FRP reinforcement ratio (0.74%, 1.16% and 1.67%), compression FRP reinforcement ratio (As' %; 25%, 40%, 100%), and both of beam width and depth (b and d). From the results; it is found that the concrete strength has a small effect on the ultimate capacity. However, the deflection is higher for beams with lesser strength. For all the cases, CFRP reinforced beams showed higher capacity and lesser ductility, while GFRP reinforced beams showed lesser capacity and higher ductility. As' ratio has insignificant effect on load capacity, but it can improve deflection; it is recommended that As' did not exceed 40% from AFRP. The beam width has insignificant effect on carrying capacity, but it decreases the corresponding deflection, while increasing the beam depth led to increase the maximum load and decrease the corresponding deflection. Comparable error is generally obtained when using the both equations of Issa and Issa (2017) and ACI440.1 (2015). [ABSTRACT FROM AUTHOR]

The steel fiber-reinforced polymer composite bars Known as (SFCB) are new kind of reinforcement, for concrete structures. A layer of glass fibers and reinforced polymer surrounding the steel bars resulting in the (GFRP), when used as concrete reinforcement contributes for enough, serviceability strength, and durability. Increasing the elastic modulus of GFRP bar, which have function of protecting corrosion in addition to reduce the initial cost of the FRP bar, is the purpose of hybridization. SFCB has the advantages of being noncorrosive, nonmagnetic nonconductive, and light in weight, along with high strength. This study presents the behavioral characteristics of RC beams, with tensile lap-spliced steel fibers—coated bars under flexure. Ten beam specimens were tested, with concrete cross-section of (25*40*420) cm and compressive strength of 30 MPa. One beam specimen, (R) was taken as reference as it was reinforced with no lap splice. Nine beam specimens were divided into three groups. Group (A) contained three beam specimens reinforced with SFCB of diameter 16 mm and lap splice of 50φ, one with stirrups, without stirrups and with staggered lap splice. Group(B) contains three beams reinforced with SFCB of 16 mm diameter and lap splice of 55 φ one with stirrups, without stirrups and with staggered lap splice. Group(C) contains three beam specimens reinforced with SFCB of 16 mm diameter and lap splice of 60 φ one with stirrups, without stirrups and with staggered lap splice. Beams were exposed to pure flexure. Crack patterns and results are presented along with stress-strain curves. Finally, conclusions are summarized and presented. [ABSTRACT FROM AUTHOR]

This study aimed to determine the strength of hollow concrete block masonry walls, beams, and columns and compare their values with brick masonry walls and ordinary reinforced concrete beams and columns. The specimens for the hollow concrete block and brick masonry walls were prepared and tested for compressive and flexural strengths and horizontal and diagonal shear strengths. Moreover, two hollow concrete blocks and two ordinary reinforced concrete beams were designed to experience flexural and shear failure and loaded under a two-point bending load. Meanwhile, a hollow concrete block and an ordinary reinforced concrete column were also constructed and subjected to centric axial loads until they collapsed. The results showed the hollow concrete block masonry walls have greater strength than those made with bricks. In contrast, both flexural and shear capacity and the flexural ductility of reinforced hollow concrete block beams were higher than ordinary reinforced concrete beams. Meanwhile, the centric compressive axial strength of the reinforced hollow concrete block column was smaller due to its inefficient bond with the infilled concrete, leading to their separation under the compressive axial load. [ABSTRACT FROM AUTHOR]

As the frequency of thermal extremes gradually increases owing to climate change, the role of thermal loads on bridge performance increasingly becomes a concern. The purpose of this study is to investigate the suitability of AASHTO Bridge Design Specifications in quantifying with confidence the design thermal gradients that account for cold wave events. An advanced finite element platform was used to model the thermal performance of a prestressed concrete box girder and to analyse the thermal gradients that occur during cold wave events. Meteorological data on four historical cold wave events in Ontario, Canada, were used as input in the thermal models to simulate the temperature distribution within the bridge deck. The temperature–time history distributions obtained were then used as boundary conditions in a structural finite element model to simulate the structural response. The thermal results indicate that the AASHTO recommended gradients failed to capture the true thermal load distribution within the superstructure, which led to an underestimation of the resulting structural implications. [ABSTRACT FROM AUTHOR]

The current camber prediction procedure in the PCI Design Handbook: Precast and Prestressed Concrete results in variations between the design and the actual camber. These variations create difficulties in maintaining the design thickness of the bridge deck and the design longitudinal profile. This research aims at enhancing the PCI design method of estimating long-term camber and deflection of prestressed concrete girders. Field measurements included monitoring cambers for a total of 94 girders from fabrication through the erection at bridge sites. Compressive strength and modulus of elasticity were measured for several girders, and the results were compared with the design properties. The differences between the design and actual concrete properties were found to be the main reason for overestimation in camber and deflection. A modification to the PCI camber prediction method is proposed to improve the accuracy of predicting the erection camber based on field measurements and material tests on four types of bridge girders. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Shear and flexural failure are commonly known as the highest catastrophic failure mode as it never gives any earlier notice before the collapse. The most common shape in the structure of beams and girders is T-section. Therefore it will be more necessary to investigate the condition of these structures. In this research, the flexural behaviour of RC T-beams is investigated experimentally and analytically strengthened with Basalt Fiber Reinforced Polymer (BFRP). A symmetrical one-point static loading system is applied on RC T-beams superficially bonded with 45° degree, and 90° wrapping up to failure. The effects of both wrapping patterns of BFRP on RC T-beams were investigated for ultimate load carrying capacity, deflection, strain, and failure modes. The experimental results demonstrate that superficially bonded BFRP can enhance the flexural capacity and reduce the deflection of the beam significantly. Further, the results show that the most effective wrapping pattern was a 45° degree than 90°wrapping and without wrapping. Then the RC T- beam was modeled by using ABAQUS to validate the present experimental and analytical results. After a series of comparative studies, the analytical results fairly admit with the experimental results. In the end, this study surmised showing different cracking patterns and yield points of the beam with and without strengthening. It is hoped that the results of this study will be of considerable help for the strengthening of T- beams and structures. [ABSTRACT FROM AUTHOR]

The current American Association of State Highway and Transportation Officials' AASHTO LRFD Bridge Design Specifications' approximate formula for estimating long-term prestress losses is the outcome of the research work presented in National Cooperative Highway Research Program report 496. It is produced by simplifying the detailed method and taking into account the variability of concrete properties and the interaction between the precast concrete girder and cast-in-place deck. This paper presents two detailed parametric studies based on the average conditions for the design and construction of commonly used bridge girders. Three spans and, consequently, three levels of prestressing for each section have been considered. The first study establishes the creep multiplier Nc, whereas the second study evaluates the shrinkage multiplier Ns. Both multipliers are used in the lump-sum formulas for estimating long-term prestress losses for different bridge girders. The multipliers produced by these studies are compared with that of the current AASHTO LRFD specifications' approximate method, and new lump-sum formulas for long-term prestress losses are proposed. [ABSTRACT FROM AUTHOR]

Accurate predictions of concrete compressive strength are critical for designers to effectively estimate the camber, deflections, and prestress losses of precast, prestressed concrete elements. A methodology that relies on regional concrete bridge girder strength test results is proposed for predicting expected concrete compressive strength. Strength data collected from precast, prestressed concrete plants were manipulated by the use of a strength-difference approach to facilitate American Concrete Institute 214R-11 analysis methods. The data set was used to evaluate five other empirical prediction model forms. When implemented using an Alabama regional data set, the methodology resulted in markedly more accurate predictions of expected concrete strength at prestress transfer and at 28 days compared with current practice. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical model of carbon fiber reinforced polymer (CFRP) retrofitted concrete beams with and without intermediate notches, developed to predict the impact load, energy response, cracking pattern and interfacial stress distribution under drop-weight impact. Considering a drop-weight falling from different heights, a CFRP sheet was bonded to the bottom surface of the beam. The specimen's drop-weight impacts were established for retrofitted and un-retrofitted simply-supported notched concrete beams. A nonlinear finite element model was developed and calibrated to analyze the interfacial stress field, failure modes, cracking patterns and damage sequences. The results obtained numerically in terms of load-time, load-displacement and energy-time curves were compared to those given by the authors' experimental tests and also to those given in the literature. For un-retrofitted beams, the impact time was very short, with failure at the center of the beam. For notched beams, the impact load decreased as notch depth increased, owing to the local loss of rigidity at the center of the concrete beam. For the retrofitted beam, however, the impact time was quite long, with a very high impact load, because the beam was more resistant, with rebound. [ABSTRACT FROM AUTHOR]

Enhancing the torsional capacity of reinforced concrete (RC) beams while maintaining reasonably economic and efficient cross-sections poses a practical challenge in the design of such elements. Thus, developing and testing economically viable reinforcing techniques for enhancing the torsional capacity of RC beams is a significant aspect. Among these techniques is the continuous spiral reinforcement system that has shown promising results in enhancing the torsional capacity of rectangular RC elements. In this study, the role of continuous rectangular spiral stirrups, as a transverse reinforcement with a controllable pitch (P) and inclination angle (θ), in enhancing the torsional behavior of rectangular solid and hollow RC beams has been investigated experimentally. The applied torque was directed to lock the spirals for all specimens. The experimental program of this investigation included testing of ten specimens of normal strength RC beams; two of which were solid with closed and spiral rectangular stirrups. While the rest of specimens were hollow specimens included one beam reinforced by closed stirrups and seven beams reinforced by rectangular spiral stirrups with different reinforcing ratios. Different variables were considered to develop a wide range of the beams' reinforcing scenarios. This includes stirrups type (conventional closed stirrups and rectangular spiral stirrups), inclined stirrups ratio, pitch, inclination angle and finally the longitudinal reinforcement ratio. In addition, a three-dimensional finite element model using ANSYS-15.0 was developed to examine the capability of the model to capture the observed torsional behavior of the experimentally tested beams. The obtained results showed that using inclined spiral rectangular stirrups in reinforcing RC solid and hollow beams greatly enhanced the torsional capacity by about 16% and 18%, respectively compared to using the conventional closed stirrups. Moreover, the results showed that using that technique leads to higher twist- angles, more ductile failure and increased strain energy by about 27% and 16% for solid and hollow beams, respectively. Lastly, the comparison between the results obtained from numerical model and experimental results showed good agreement and thus the numerical model can be used to extend the experimental work for investigating different reinforcing schemes. [ABSTRACT FROM AUTHOR]

This study presents an artificial intelligence-based model to predict the flexural strengthening of RC beam/slab strengthened with UHPC (RC-UHPC) and perform uncertainty quantification of such values. Improved eliminate particle swamp optimization hybridized artificial neural network (IEPANN) was a model developed on artificial neural network (ANN) optimized by improved-eliminate-particle-swamp optimization (IEPSO). Experimental datasets were used to establish the hybrid ML model. The efficiency of IEPANN was compared against support vector regression (SVR) and multiple linear regression (MLR). The IEPANN demonstrates outstanding performance over MLR and SVR. The flexural strengthening of RC-UHPC depends on materials and geometrical configurations, which have stochastic characteristics. Convergence studies, sensitivity, and probabilistic analyses were conducted on each random parameter. Simulation results indicated that strengthening configuration is the most sensitive to flexural strengthening. Systematic assessment of uncertainties in flexural strengthening may lead to a higher confidence level in model outcomes, and RC-UHPC is examined and designed. It enhances construction reliability. [ABSTRACT FROM AUTHOR]

Concerns about corrosion damage have been intensified due to the failure in marine structures and bridges. In this study, several simulations and tests have been accomplished to investigate the effect of corrosion on bending and shear capacities of reinforced concrete beams. By using ABAQUS software, this research is set to analyze the other effects of corrosion on reinforced beams. The accuracy of simulation results has been verified by existing experiment results. Several concrete beams with different degrees of corrosion are modeled in ABAQUS software. The results of simulation were compared with experimental results. Moreover, force-displacement diagrams are produced to investigate the corrosion effects more precisely. This study investigates effects of corrosion location, amount and intensity of corrosion, concrete compressive strength, and bar yielding stress on reinforced concrete beams strength. Furthermore, the effects of different locations and different corrosion degrees in steel rebar area and integration between steel and concrete are evaluated due to corrosion. Results demonstrate that corrosion effect on the loading capacity of beams in the tension region is greater than that in the compressive part. Furthermore, the corrosion around support regions is remarkable. [ABSTRACT FROM AUTHOR]

Nanjing Jiangxinzhou Yangtze River Bridge is located in Nanjing, China. Its main bridge across the river is a central double-cable plane three-tower cable-stayed bridge. It is the world's first all-steel-concrete composite cable-stayed bridge with a span layout of 80 + 218 + 600 + 600 + 218 + 80 = 1796 m, pioneered the steel shell-concrete composite structure tower, developed coarse aggregate reactive powder concrete(CA-RPC), and applied it to the main girder of the bridge, forming a lightweight high-performance steel-coarse aggregate reactive powder concrete composite beam. Steel stranded stay cables are also applied to the bridge. The main span of the bridge across the embankment is 78 m prestressed continuous box girder with prestressed corrugated steel webs, and the segmental prefabrication construction technology is adopted for the first time; the south and north approach bridges adopt segmental prefabrication and prestressed concrete box girder. Nanjing Jiangxinzhou Yangtze River Bridge takes industrial construction as the main principle of the structural design consideration and has achieved numerous original technologies in new materials, new structures, and new technologies. This paper will systematically and comprehensively introduce the design standards of the bridge, the overall design of the main bridge, and the development of key components. The design overview of the bridge across the embankment is also attached for further reference. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Horizontally curved bridges have been mostly built with steel plate I-girders or tub girders. In the past 15 years, curved concrete girders have been successfully used in several states, including Nebraska, Colorado, and Florida. This paper addresses the design of curved concrete girder bridges using ultra-high-performance concrete (UHPC) by combining state-of-the-art spliced girder technology and UHPC technology. It also proposes a number of unique features that result in further simplification of precast concrete production and construction. Critical design criteria are discussed. The system development of curved UHPC girder bridges and necessary construction steps are elaborated through a numerical example of a three-span bridge, which shows greatly reduced concrete quantities when compared with recently constructed curved concrete girders. With UHPC designed as proposed here, horizontally curved bridges are expected to be cost competitive with conventional concrete and more economical than structural steel. [ABSTRACT FROM AUTHOR]

Structural behaviour of steel fibre reinforced concrete members depends on different parameters such as aspect ratio of fibre, the geometrical shape of fibre and placement of fibre in concrete. Incorporation of fibres in concrete has helped in arresting cracks in concrete and enhancing its capacity. Materials like steel, glass and organic polymers are used to produce fibres suitable for reinforcing concrete. During construction of complex structure first task is to identify the appropriate fibre and its effects on structures. As per the requirement of structure we have to select fibre and have to analyse the consequences after implementation such as cracks. Steel fibre usage percentage and aspect ratio two main parameter which must be integrated with concrete. The main objective of this investigation is to determine two prime parameters compressive total creep and tensile total creep of high-strength concrete beams at long term under following conditions of steel fibre dosage and steel fibre aspect ratio. [ABSTRACT FROM AUTHOR]

Pretensioned concrete beams are widely used as bridge girders for simply supported bridges. Understanding the fatigue behavior of such beams is very important for design and construction to prevent fatigue failure. The fatigue behavior of pretensioned concrete beams is mainly influenced by the fatigue of the prestressing strands. The evaluation of previous test results from the literature indicated a reduced fatigue life in the long-life region compared with current design methods and specifications. Therefore, nine additional high-cycle fatigue tests were conducted on pretensioned concrete beams with strand stress ranges of about 100 MPa (14.5 ksi). The test results confirmed that current design methods and specifications overestimate the fatigue life of embedded strands in pretensioned concrete beams. [ABSTRACT FROM AUTHOR]

To improve the accuracy of predicting the shear bearing capacity of prestressed high-strength concrete beams with web reinforcement, shorten the prediction time, and improve the quality of engineering construction, a BIM model is proposed to predict the shear bearing capacity of prestressed high-strength concrete beams with web reinforcement. For the first time, specimens of prestressed high-strength concrete beams with web reinforcement were made, and their mechanical performance parameters, test points, and loading schemes were determined; Secondly, use the MCT file in Midas Civil to create a finite element model, and then combine the revit parameter model method to establish a BIM based finite element model; Finally, through the data conversion program between the created Revit model and ANSYS, a BIM based mechanical analysis model is generated to predict the shear bearing capacity of prestressed high-strength concrete beams with web reinforcement. The results show that this method can obtain high-quality three-dimensional renderings, with a standard deviation of 0.118 between the predicted shear bearing capacity and the experimental value, and a prediction time of about 0.5 s, which is lower than the expected results. This method has high prediction accuracy and efficiency, which can provide reliable technical reference for construction projects and improve the safety of building structures. [ABSTRACT FROM AUTHOR]

To explore the vulnerability of a reinforced concrete girder bridge and reinforced concrete building during an earthquake, and to compare the difference in the seismic capacity of the two types of engineering structures, the nonlinear vulnerability numerical and probabilistic model analysis methods were combined. Overall, 1069 reinforced concrete girder bridges and 949 reinforced concrete buildings damaged in the Wenchuan earthquake of May 12, 2008 were selected for vulnerability analysis. The vulnerability grades of damaged samples were evaluated according to the Chinese seismic intensity scale (CSIS-08), and the vulnerability matrix of reinforced concrete girder bridges and reinforced concrete buildings in multiple intensity regions was established. Moreover, the novel vulnerability comparison curve model was developed by considering the failure ratio and exceeding probability. The anomaly characteristics of seismic damage vulnerability between reinforced concrete girder bridges and reinforced concrete buildings under the influence of age, seismic design, the coupling of age and seismic design, and foundation type factors were compared and analysed. By employing the matrix calculation model of the mean damage index, the matrix and curve comparison model of the mean damage index vulnerability parameters of reinforced concrete girder bridges and reinforced concrete buildings in multiple intensity zones were developed. [ABSTRACT FROM AUTHOR]

Hybrid use of Carbon fiber reinforced polymer (CFRP) composites with conventional construction materials offers an ample opportunity to develop economical and high-performance structures. However, anchoring and debonding problems remains a challenge for the accomplishment of this technique. In this study, a novel application was implemented in which the CFRP sheet was integrated as internal flexural reinforcement for RC beams. The target was to evaluate the contribution of the CFRP sheet to the flexural performance and thus assess the efficiency of using the CFRP sheet as primary or supplemental flexural longitudinal steel reinforcement. CFRP sheet can be cut without difficulty to any width/length and then attaching them to the main steel bars without using epoxy. Similar to the longitudinal steel reinforcement, the CFRP strips work integrally with steel reinforcement as the concrete confines them. The investigated parameters are the number of CFRP layers, CFRP sheet length, strengthening type (internal or external strengthening). Therefore, the feasibility of internal strengthening for improving the behavior of RC beams is of vital interest. The performance of each beam was evaluated in terms of failure mode, load versus mid-span deflection curve, ultimate deflection, ultimate load capacity, stiffness, displacement ductility index, energy absorption, energy absorption ductility index, performance factor, and CFRP strain. The results show a significant improvement in the majority of the investigated parameters and show the effectiveness of internal strengthening. The internal strengthening provided external cracks arresting mechanism and even after reaching the ultimate load capacity. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The deterioration of lightweight concrete (LWC) members due to intensive fires, necessitate the development of strengthening techniques for extending their service life. Fourty reinforced concrete (RC) beams were cast, heated at 600 °C for 3 hrs., strengthened using polymeric sheets (FRP), for regaining their flexural capacity. The flexural behavior of the beams investigated including the ultimate load, stiffness, deflection, and cracking pattern were described. The heated LWC reinforced beams regained a large portion of their load capacity, and exhibited typical flexural cracks in the pure bending zone, and flexure-shear cracks in the shear span, after strengthening. Among the strengthening schemes proposed, using a single layer and U shaped jacket of FRP sheets at the bottom, and sides of the beams, was effective for regaining their full flexural capacity. The experimental results indicated that FRP laminates can be considered as a promising material for maintenance and rehabilitation of heat damaged LWC members. [ABSTRACT FROM AUTHOR]