Ordinary Concrete Beams Research Articles

A Review on Mechanism and Influencing Factors of Shear Performance of UHPC Beams

Ultra-High-Performance Concrete (UHPC) is increasingly used in various engineering projects due to its exceptional mechanical properties. This work conducts a literature review of research on the shear performance of UHPC beams in recent decades, with a focus on summarizing the formulas for calculating shear capacity and the main factors influencing shear performance. Firstly, this work reviews the calculation methods for the shear capacity of UHPC beams in different countries, along with their respective advantages and limitations. Subsequently, it provides a detailed analysis of various factors influencing the shear performance of UHPC beams, including longitudinal and stirrup reinforcement, steel fiber content, aggregates, admixtures, the shear-span ratio, shear keys, bolts, shear-reinforcement techniques, and environmental impacts. Through horizontal comparisons, the performance of UHPC beams and ordinary concrete beams under similar experimental conditions is examined to reveal the optimal shear working conditions for UHPC beams. Additionally, it is found that UHPC performs exceptionally well in composite beams, being compatible with numerous materials and significantly enhancing the shear strength of these beams. Lastly, the paper proposes suggestions for maximizing the shear performance of UHPC beams within a safe and reliable operating range and outlines future research directions.

Shear Behavior of High-Strength and Lightweight Cementitious Composites Containing Hollow Glass Microspheres and Carbon Nanotubes

In this study, an experimental program was conducted to investigate the shear behavior of beams made of high-strength and lightweight cementitious composites (HS-LWCCs) containing hollow glass microspheres and carbon nanotubes. The compressive strength and dry density of the HS-LWCCs were 87.8 MPa and1.52 t/m3, respectively. To investigate their shear behavior, HS-LWCC beams with longitudinal rebars were fabricated. In this test program, the longitudinal and shear reinforcement ratios were considered as the test variables. The HS-LWCC beams were compared with ordinary high-strength concrete (HSC) beams with a compressive strength of 89.3 MPa to determine their differences; the beams had the same reinforcement configuration. The test results indicated that the initial stiffness and shear capacity of the HS-LWCC beams were lower than those of the HSC beams. These results suggested that the low shear resistance of the HS-LWCC beams led to brittle failure. This was attributed to the beams’ low elastic modulus under compression and the absence of a coarse aggregate. Furthermore, the difference in the shear capacity of the HSC and HS-LWCC beams slightly decreased as the shear reinforcement ratio increased. The diagonal compression strut angle and diagonal crack angle of the HS-LWCC beams with shear reinforcement were more inclined than those of the HSC beams. This indicated that the lower shear resistance of the HS-LWCCs could be more effectively compensated for when shear reinforcement is provided and the diagonal crack angle is more inclined. The ultimate shear capacities measured in the tests were compared with various shear design provisions, including those of ACI-318, EC2, and CSA A23.3. This comparison showed that the current shear design provisions considerably overestimate the contribution of concrete to the shear capacity of HS-LWCC beams.

Shear Performance and Damage Characterization of Prefabricated Basalt Fiber Reactive Powder Concrete Capping Beam Formwork Structure

Basalt Fiber Reactive Powder Concrete (BFRPC) semi-prefabricated composite capping beam structures can effectively improve the shortcomings of ordinary concrete capping beams' construction difficulties and insufficient bearing capacity. In this study, with the objective of analyzing the shear damage and damage characteristics of a prefabricated BFRPC capping beam formwork, structural damage tests under different levels of loading were carried out to obtain the mechanical parameters of key nodes. Acoustic emission (AE) and Digital Image Correlation (DIC) techniques were used to acoustically and visually characterize the formwork damage. The research results showed that the damage stage of the capping beam formwork was divided, and an early damage warning method was proposed based on the acoustic parameters. Using the DIC technique to identify the crack width evolution pattern during the shear process, it was found that the cracks expanded steadily as the load increased. Combining the experimental and simulation results as well as the Subdivision Superposition Theory, a half-open stirrup strength discount factor β was introduced and suggested to take a value of 0.79. The formula for calculating the shear capacity of BFRPC capping beam formwork is proposed to provide a theoretical basis for its application in prefabricated assembled structures.

Impact characterization of coral aggregate reinforced concrete beam: A 3D numerical study

Coral aggregate concrete (CAC), an innovative construction material, utilizes abundant marine resources, including coral aggregates and seawater. In the realm of reef engineering, CAC is widely used in structural elements such as reinforced beams and columns. This paper presents a three-dimensional (3D) mesoscale model to assess the impact behavior of coral aggregate reinforced concrete beams (CARCB), incorporating the heterogeneity characteristics of CAC and the explicit simulation of reinforcement components. The 3D mesoscale modelling approach developed in this paper was validated by previous experimental data of CARCB, and used for extensive parametric studies evaluating effects such as concrete strength grade, reinforcement ratio, and impact velocity on the static and dynamic bending behaviors of CARCB. Finally, based on the mesoscopic cracking process and damage patterns of CARCB under static and dynamic loads, this study illustrates the corresponding macroscopic mechanical behaviors and failure mechanisms. Results indicate that the predominant forms of flexural failure in CARCBs are tensile cracking in the mid-span region and diagonal shear cracking. Results demonstrate that the predominant forms of flexural failure in CARCBs are tensile cracking in the mid-span region and diagonal shear cracking. Specifically, local bending failures and symmetrical diagonal shear cracks were evident in the CARCBs subjected to dynamic loads, closely resembling those in ordinary concrete beams. With increasing concrete strength grades (C30 to C60) and reinforcement ratios (0.9 %–1.7 %), a significant reduction in the mid-span ultimate deflection of CARCB is observed, indicating enhanced impact resistance. Additionally, as the impact velocity increases from 1 m/s to 50 m/s, the mid-span ultimate deflection of CARCB is magnified by a factor of approximately 200, indicating intensified dynamic damage to CARCB with increasing impact velocities.

Parametric study, finite element analysis, and load capacity calculation for flexural behaviour of seawater and sea sand concrete beams reinforced with GFRP bars

This study sought to enhance the understanding of seawater sea sand concrete (SWSSC) structures reinforced with glass fiber-reinforced polymer (GFRP) bars. To achieve this, an experimental investigation was conducted involving the production and testing of 6 GFRP bar-reinforced SWSSC beams (GFRP beams) alongside 3 ordinary seawater sea sand concrete (OSWSSC) beams (Ordinary beams) to evaluate their flexural performance. Additionally, a subsequent analysis comprised the establishment of 11 full-scale finite element models aimed at parameter assessment on GFRP beams. The experimental and numerical findings revealed that an increase in sea sand replacement ratio in SWSSC beams, with a shear-span ratio of 2.2, led to varying degrees of shear-compression failure. Notably, owing to the superior crack resistance of SWSSC, the beams demonstrated outstanding structural coordination. Compared to OSWSSC beams, GFRP beams with a 100 % replacement ratio of sea sand or an increased in concrete strength to C55 had initial stiffness values that were 150 % and 106 % larger, respectively. Further investigation unveiled that a reduction in the shear-span ratio from 2.5 to 1.0 or an increase in the longitudinal reinforcement ratio from 1.27 % to 2.53 % significantly augmented the ultimate load-carrying capacity, resulting in increases of 88.0 % and 37.7 %, respectively. Based on these findings, several design recommendations are proposed: 1. Establish a deflection limit at l0/500 or implement more stringent measures for GFRP beams. 2. Consider reducing the diameter of GFRP bars while maintaining a 50 % sea sand replacement rate to mitigate crack formation. 3. An excessive longitudinal reinforcement ratio hampers the enhancement of specimen load-carrying capacity. 4. Consider utilizing Chinese specifications for flexural capacity calculations.

Experimental and numerical research on shear performance of GFRP bar reinforced seawater sea-sand concrete deep beams without stirrups

Using glass fibre-reinforced polymer (GFRP) bars to reinforce seawater sea-sand concrete (SWSSC) is a feasible way to replace traditional concrete structures. Thus, this paper aims to understand the shear response of GFRP bar-reinforced SWSSC (GFRP-SWSSC) deep beams. Experimental and numerical programs were carried out on four-point shear tests of GFRP-SWSSC deep beams without stirrups. Seventy specimens were tested to investigate the effects of key parameters on shear responses, including concrete categories, seashell content, section heights, and GFRP bar diameter. The test results indicated that the cracking strength of GFRP-SWSSC deep beams was slightly higher than ordinary concrete deep beams. The increased section height of GFRP-SWSSC deep beams and the decreased shell content remarkably enhanced the stiffness and shear ultimate strength. The corresponding finite element model (FEM) of GFRP-SWSSC specimens was established and validated by comparison with test results. Further, three guidelines predictions for the shear strength of GFRP-SWSSC beams were too conservative. The new design formulae derived from modified tension-compression theory were put forward to evaluate the shear strength of GFRP-SWSSC deep beams, and the comparisons demonstrated that the proposed design formulae achieved sufficient accurate predictions for practical engineering. Based on research on shear performance, the hybrid GFRP-SWSSC structure is a feasible solution to resource shortages, which provides a promising application prospect in marine engineering.

Innovative Method for Reinforcing Beams with Different Types of Concrete Using Cross-Rod Steel Bracing Under Pure Torsion

This study aimed to investigate the effectiveness of an innovative way to reinforce the concrete beams using cross-rod steel bracing under pure torsion. The experimental program consists of casting and testing eighteen concrete beams made of three types of concrete in the form of three groups, with the same dimensions for all beams (200×200×2000) mm. The parameters of the study included concrete types (normal strength, high strength, and steel fiber), as well as the number of internally cross rods (4, 8, 12, 16, 20). The experimental results showed that the number of internally cross-rod reinforcements and concrete type had an effect on ultimate torque, crack width, toughness, and stiffness. The torsional capacity of all concrete beams increased with the increase in internally cross-rod reinforcement. The ultimate torque of normal-strength concrete beams, high-strength concrete beams, and steel fiber concrete beams reinforced with twenty internally cross rods increased (88.34%, 53.20%, and 40.60%), respectively, compared to beams without cross rods in each type of concrete beam. Increasing the internally cross rod in all concrete beams effectively inhibited the development of crack width and improved torsional stiffness, especially in fibrous concrete beams that contained steel fiber. The torsional toughness of all concrete beams increased with the increase of internally cross-rod reinforcement, and it was higher in steel fiber concrete beams. The steel fiber concrete beams reinforced with internally cross-rod steel bracing have better torsional properties compared to ordinary concrete beams and high-strength concrete beams. Doi: 10.28991/CEJ-2024-010-04-06 Full Text: PDF

Experimental and Numerical Study on the Flexural Behaviors of Unbonded Prestressed I-Shaped Steel Encased in Ultra-High-Performance Concrete Beams

A novel type of traditional composite member-unbonded prestressed I-shaped steel encased in a UHPC (PSRUHPC) beam is proposed to reduce the brittleness of UHPC beams and improve their bearing capacity. A PSRUHPC beam, an unbonded prestressed UHPC (PRUHPC) beam, and an I-shape steel UHPC (SRUHPC) beam were manufactured, and their flexural static performances were assessed using a flexural comparison test. The test results reveal that the flexural process of the PSRUHPC beam is similar to that of ordinary reinforced concrete beams, and UHPC crushing in the compression zone is a sign of failure. Due to the bridge coupling effect of steel fiber, the crushed concrete still maintains good integrity without bursting, the UHPC in the tension zone remains functional after cracking, and the cracking inflection point of the load–deflection curve was not obvious. The PSRUHPC beam showed a significantly improved bearing capacity and flexural stiffness, its load–deflection curve exhibited significantly more energy consumption, and its bending ductility performance was improved, with better deformation properties. Compared with PRUHPC beams, PSRUHPC beams show a bearing capacity increase of 55.3%, a cracking load increase of 11.9%, and a displacement ductility coefficient increase of 76.2%. Compared with SRUHPC beams, PSRUHPC beams show a 15.4% increase in bearing capacity, a 50.2% increase in cracking load, and a 12.1% increase in displacement ductility coefficient. The application of prestress can significantly improve the stiffness of the beam prior to cracking. The cracking loads of prestressed ordinary concrete beams and steel-reinforced concrete beams account for 20–30% of their ultimate loads, which value was 40–50% for the tested beams. The change trend of strain in the section steel and UHPC is roughly the same at the same height, and the strains of the two deviated after most of the section steel yielded under tension, but they can generally work together. When the tested beams were cracked, multiple cracks appeared, which were fine and dense. The magnetic flux sensor cable force-monitoring system can better monitor the strand stress increment of unbonded prestressed steel UHPC beams, where the prestressed strand did not yield tension under the final state; the load–strand stress increment curve was basically the same as the load–deflection curve, and the stress increment of the unbonded steel strand positively correlated with the midspan deflection. Finite element simulation was used to verify the test results, and we determined the reinforcement ratios for non-prestressed and prestressed reinforcement, as well as the ratio of a steel-containing section, the effective prestress, the height of prestressed reinforcement, the position and strength of I-shaped steel, and whether or not the prestressed reinforcement was bonded. The effects of these parameters on the bearing capacity and displacement ductility coefficient of PSRUHPC beams were studied. The results can provide a reference for subsequent theoretical design calculations.

Experimental research on mechanical properties of simply composite beam with reactive powdered concrete considering the shear slip effect

To evaluate the effectiveness of reactive powder concrete in practical applications, this study focuses on analyzing the mechanical properties of composite beams reinforced with reactive powder concrete under concentrated forces. By employing the principles of elastic mechanics, an analytical solution is derived for double-layer reactive powder concrete laminated beams subjected to vertical concentrated forces. The obtained deflection curve equation provides valuable insights into the behavior of double-layer laminated beams. The study investigates the stress performance of concrete beams reinforced with reactive powder concrete through static load tests. The tests include ordinary reinforced concrete beams, ordinary concrete reinforced beams, and steel fiber reactive powder concrete reinforced test beams. The experimental results demonstrate that the load capacity of ordinary concrete beams can be significantly improved by strengthening them with RPC. The strain distribution along the height of the section follows the assumption of a flat section, and the failure pattern of the reinforced test beam is similar to that of the ordinary concrete beam. Therefore, it is feasible to predict the results and phenomena of the composite beam by analyzing the stress in an ordinary reinforced concrete beam. Shear slip occurs at the interface of different materials under stress due to the reinforcement layer. The test results also indicate that special attention should be given to the beam body's fulcrum and the shear member's quart.

Long-term performance of basalt fibre-reinforced marine geopolymer concrete in harsh environment

The current study reports on the long-term structural performance of novel reinforced marine geopolymer concrete beams under accelerated weathering conditions. The study covers the flexural performance of 40 geopolymer concrete beams reinforced with basalt fibre-reinforced polymer (BFRP) bars, including 12 beams under sustained loading when exposed to 3, 6 and 12 months of accelerated marine environment consisting of tidal cycles of seawater at a temperature of 50°C. The experimental results revealed that the novel marine geopolymer concrete reinforced with BFRP bars reported minimal micro- and macro-mechanical degradation compared to geopolymer concrete or ordinary concrete beams under the same exposure environment, with and without sustained loading. The BFRP-reinforced self-compacting geopolymer concrete (SCGC) beams reported 87% residual ultimate load after 12 months of exposure to marine environments, while the sustained loaded BFRP-SCGC beams reported a residual strength of 79%. In addition, microstructural assessment using scanning electron microscopy and energy dispersive X-ray spectroscopy analysis revealed that after 12 months of exposure there was a trace of chloride salts, indicating the chemical ingress over time; however, the impact on structural properties is not distinct.

An experimental study of bending resistance of multi-size PFRC beams

Abstract To study the effects of macro- and micro-fiber on the concrete beams, bending resistance tests were conducted on the polypropylene fiber-reinforced concrete beams. Stepwise loaded tests were carried out to obtain the load–deflection curves for different test pieces, cracking load values of the first inclined crack, recording and depicting crack development, changes in mid-span deflection of the test pieces, load–strain relationships of concrete, etc. The crack patterns and failure modes were observed. The research findings have shown that the ultimate load of the concrete beams doped with multi-size polypropylene fiber is 58.31 and 34.08% higher than that of ordinary concrete beams and concrete beams with single macro-fiber, respectively. Notably, the ultimate anti-bending bearing capacity of the beams significantly improves following the addition of macro-fiber. Polypropylene fiber can offset the defects caused by macro-fiber, remarkably suppress the development of cracks, and control the deformation of beams due to the effects of micro-fiber of different dimensions.

Experimental study of a composite beam externally bonded with a carbon fiber-reinforced plastic plate

According to the characteristics of steel fiber reinforced concrete (SFRC) with high tensile strength and carbon fiber reinforced plastic (CFRP) with high strength and light weight, a composite beam composed of CFRP plate, SFRC and ordinary concrete (OC) is developed in the paper. Eight specimens, including four CSOCBs with different heights of the SFRC and four SFRC–OC composited beams with varying heights of the SFRC, were tested to analyze the flexural behavior. The results show that the composite beam composed of OC, SFRC and CFRP improves the ultimate load capacity of the beam under unidirectional load, enhances the cracking and deformation resistance of the beam, and solves the defects of the weak tensile capacity of ordinary concrete beams. Applying them to the building structure can improve the stability of the structure and prolong the service life of the building. A prediction model for the bending capacity of the CSOCB was proposed and validated. Based on the limit state design method, the design formula for the bending capacity of the composite beam is described in detail herein.

Flexural behavior of steel fiber-reinforced coal gangue aggregate concrete beams

The flexural behavior of steel fiber-reinforced coal gangue aggregate concrete (SFCGC) and steel fiber-reinforced ordinary concrete (SFOC) beams were investigated in this study. 11 specimens were tested using four-point bending tests to investigate the effect of coal gangue replacement rate (CGRR) (0%, 50%, 100%), steel fiber volume content (SFVC) (0%, 0.5%, 1%, 1.5%), rebar ratio (0.6%, 1.17%, 1.94%), and beam height (200 mm, 300 mm) on the beam flexural performance. The failure modes, flexural capacities, flexural stiffness, ductility, and energy dissipation coefficient of the specimens were analyzed. In addition, the stress-strain curve of SFCGC was obtained by axial compressive tests in this study. A equations for the stress-strain relationship of SFCGC beams were obtained by data fitting. a finite element model (FEM) of SFCGC beams was established in ABAQUS. A self-programmed Python script was used to create the steel fiber model in FEM of an SFCGC beam, in which steel fibers were distributed randomly and discretely to investigate the strengthening effect of steel fibers on SFCGC beams. Finally, a comparative analysis shows good agreement in the load-deflection curves and transverse strain obtained from simulations using the established FE model and tests.

Flexural Behavior of Graphite Tailings RC Beams in Chloride Environment

This paper investigates the mechanical properties of graphite tailings concrete beams under various curing environments. The results show that the concentration of graphite tailings has an important influence on the mechanical properties of concrete. Finally, the bending characteristics of the beam and the modified bearing capacity calculation formula are obtained, which provides a theoretical basis and the reference value for the construction of green building materials. Through research, the main innovations and main findings of this paper are as follows: (1) In the three kinds of concrete experimental environment, the fracture load and ultimate load of concrete beams with graphite tailings replacement rate of 20% are the largest. (2) In the three kinds of concrete test environment, when the concrete test beams under the same load, with the increase of graphite tailings replacement rate, the mid-span deflection of concrete beams showed a trend of decreasing first and then increasing. When the replacement rate of graphite tailings sand is 20%, the mid-span deflection of the test beam is the smallest. (3) Through experiments, it is found that the normal section bearing capacity of graphite tailings concrete beams after chloride salt erosion conforms to the plane section assumption. After chlorine salt erosion, the strain of the longitudinal tensile steel bar of concrete beams with different graphite tailings sand replacement rates is the same as that of ordinary concrete beams, and the slope of the strain curve is the same, showing a linear trend. The experimental results show that the replacement rate of graphite tailings sand has an insignificant effect on the strain of steel bars. (4) The Gauss function is used to fit the experimental value of normal section bearing capacity of concrete beam, and the calculation formula of normal section ultimate bearing capacity of graphite tailings sand concrete beam under chloride environment is established. The research results of this paper have significant reference value for the study of mechanical properties of graphite tailings sand concrete components.

Flexural capacity prediction of steel fiber reinforced concrete beam with recycled fine and coarse aggregate

In this study, the flexural performance of the steel fiber reinforced concrete beams with recycled fine and coarse aggregates was investigated through the experiments. The effects of steel fiber volume fraction, recycled fine and coarse aggregate replacement ratio, and concrete compressive strength grade on the flexural performance of steel fiber reinforced recycled aggregate concrete (SFRAC) beams were systematically studied in terms of failure mode, flexural capacity, cracking patterns, load-deflection response, and load-tensile reinforcement strain response. The results showed that the flexural capacity and deflection of beams increased and decreased with the increase of steel fiber volume fraction, respectively. The beam with 100% replacement ratio of recycled fine aggregate and 0.5% volume fraction of steel fiber presented the similar or even better flexural performance than that of the ordinary concrete beam. By adding 1.0% volume fraction of steel fiber, the flexural capacity of beam with both 100% replacement ratio of recycled fine and coarse aggregates was higher than that of the ordinary concrete beam. Based on the experimental results of SFRAC beams in this study and other literature, the effects of steel fiber volume fraction and recycled aggregate replacement ratio on the flexural capacity of beams were quantitatively analyzed. Lastly, a model for the prediction of SFRAC beam flexural capacity was proposed and verified.

Flexural Performance of Sustainable Fly Ash Based Concrete Beams

The demand for concrete is high due to its solid strength and flexibility. To produce more concrete requirement of cement is very large. The production of concrete releases CO2 into the atmosphere. This can lead to global warming. By including other substances that have a cementations tendency, cement consumption can be decreased. To lower the cement consumption in concrete, a variety of pozzolanic ingredients are being used. It is being investigated whether fly ash can replace cement. Flexural tests were performed on reinforced concrete beams with fly ash contents ranging from 0% to 60% and binder contents of 400 and 450 kg/m3 with a water binder ratio of 0.4. The beam size is 100X200mm with a length of 1.2 m. It was observed that all the beams failed under compression in both mixes. In both, the mixer’s depth of crack is reduced when compared with the fly ash incorporated beams with no-fly ash concrete beams. The quick spread of the fracture is slowed down by the addition of fly ash to concrete. The filler effect, which aids in pore refinement and prevents the creation of cracks as well as the enlargement of propagated cracks, is initiated in the concrete as the fly ash content rises. According to the experimental findings, the load capacity of RC beams containing 30% fly ash is the greatest of all the beams. The outcomes for exhibit the same behaviour. Compression resistance. Finally, it was shown that, versus ordinary concrete RC beams, the inclusion of fly ash boosted the beam’s capacity to carry loads by up to 40% fly ash replacement. Whenever the fly ash content is increased by up to 40% replacement, the RC beam’s final deflection increases.

Mechanical properties of engineered cementitious composite using polyvinyl alcohol fibers

Engineered Cementitious Composite (ECC) is an advanced construction material that combines cement, fine aggregates, and specially designed fibers to create a highly ductile and durable building material. ECC is renowned for its exceptional tensile strain capacity, allowing it to undergo significant deformation while retaining its structural integrity. This characteristic makes ECC particularly suitable for applications where flexibility and durability are paramount, such as in earthquake-resistant structures and infrastructure repairs. This study investigates the tensile and flexural properties of ECC using Polyvinyl Alcohol Fibers (PVA) and compares these properties with those of regular mortar. Various sizes of PVA are available, and for this study, we utilized 12mm PVA fibers. The trial concrete mix design used was M30, with a watercement ratio of 0.3. The mixing process for traditional concrete and ECC is similar. Initially, the dry combination of ingredients is mixed for one to two minutes, followed by the addition of High Range Water Reducer (HRWR), and the mixture is further stirred for an additional three minutes. Finally, fibers are incorporated to achieve a stable condition for mixing. The samples used for testing consisted of 15 beams and 15 cylinders. The beam dimensions were (500 X 100 X 100) mm, while the cylinder dimensions were 100 mm in diameter and 200 mm in height. These samples were tested after 28 days of curing. The experimental findings indicate that PVA-enhanced concrete exhibits greater tensile and flexural strength when compared to conventional concrete, with results varying based on the percentage of PVA used. The split tensile strength of 1.5% PVA ECC cylinders was enhanced by approximately 46.8%. In terms of flexural strength, there was a decrease observed in 0.5% and 1% PVA fiber beams compared to ordinary concrete beams. However, the 1.5% PVA fiber beam exhibited a 43.45% improvement over the 0% fiber beam and showed a 9.4% increase compared to the 2% PVA beam. Additionally, the 1% PVA sample in the soundproof test reduced sound by up to 21.2%.

Statistics and Analysis of Steel-Concrete Composite Simply Supported Box Girder Bridges in china

This paper collects the basic information of steel-concrete simply supported box girder bridges in China, analyzes And Summarizes its design parameters such as span, height-to-span ratio, bridge width, steel bottom plate thickness, steel web thickness, concrete roof thickness, and material grade. The results show that compared with the ordinary concrete beam bridge, the steel-concrete composite simply supported box girder bridge has a 70% reduction in web weight, and has a stronger spanning ability,and has a Lower beam height under the same span. The correlation equation between height-span ratio and span is fitted, which can be used as a reference for future design research of steel-concrete composite simply supported box girder bridges.

Shear Behavior of Granulated Blast Furnace Slag-Based Geopolymer-Reinforced Concrete Beams

Active research is ongoing regarding the mechanical behavior of structural members manufactured from geopolymer concrete (GC), as it lacks standardized/codified manufacturing and design procedures. This study aims to address the shear behavior of GC beams. First, a consistent trial–error-based approach was used to develop the optimal mixture ratio (102.38/234.0 for NaOH/Na2SiO3) in terms of workability and consistency for the production of six (6) test specimens with span-to-depth ratios of (a/d) of 2.5, 3.5, and 4.5 and transverse reinforcement intervals of 10, 15, and 20 cm. Then, shear failure tests using a three-point bending setup were conducted and analyzed statistically. As a first attempt in the literature, an empirical expression for shear capacity prediction that was specifically tuned for GC beams was given. This expression, along with seven other similar expressions for ordinary concrete beams from the literature, and various practice codes were tested against a pool of experimental shear failure results given by four (4) different researchers. As a measure of the predictive capability, coefficient of variation (COV = standard deviation/average) values were obtained, and the lowest COV value of 0.305 suggested that the expression obtained the highest predictive capability, whereas more common practice codes such as ACI318, EN1992, and ENV1992 produced COV values of 0.435, 0.374, and 0.627, respectively. Finally, this study provides a working expression for the shear capacity estimation of GC beams and a mixture ratio for the practical manufacturing conditions of workability and consistency, with a slump value of 270 mm and a 90 min setting time.

Experimental Study on Flexural Behaviour of Prestressed Specified Density Concrete Composite Beams

To solve the problem of poor seismic resistance due to the disadvantages of traditional concrete composite beams, such as heavy self-weight in prefabricated buildings, prestressed specified-density concrete composite beams are proposed herein. First, a mix ratio test of specified-density concrete was performed. Second, five prestressed specified-density composite beams, a prestressed ordinary concrete composite beam, and a prestressed semi lightweight concrete cast-in-situ beam were tested. The influence of the precast concrete height, reinforcement ratio, and concrete materials on the failure mechanism, flexural bearing capacity, and short-term stiffness of the composite beams were analysed. From the results, the specified-density concrete composite beams and the ordinary composite beam had similar ultimate bearing capacities, but the average distance between crack spacings of the former was smaller. The precast concrete height affected the bending performance of the prestressed specified density concrete composite beam insignificantly, but the maximum ultimate bearing capacity of the composite beam could be increased by 35.6% by increasing the reinforcement ratio. The composite beam and the cast-in-place beam exhibited similar load-carrying capabilities and deformation properties. The average crack spacing, cracking load, and ultimate load value of the specified density concrete composite beams calculated according to the China national standard “Code for design of concrete structures” were consistent with the measured values.