Clear Span Research Articles

Structural response of precast reinforced concrete structure with emulative moment connections under internal column loss scenarios

Depending on the design, the connections of precast concrete (PC) structures can be susceptible to severe damage under large deformation. Consequently, PC structures may behave differently from cast-in-situ reinforced concrete (RC) structures under column loss scenarios. This study focuses on a class of PC structures that utilize splice sleeves (SSs) to assemble the precast components with integrated beam-column connections (IBCCs). This PC design can alleviate rebar congestion issues and minimize the need for post-cast concrete in the connection regions during assembly. The IBCCs are typically designed to mimic the behavior of corresponding RC connections under service loading conditions. However, the extent of structural emulation under column loss scenarios is not immediately clear. In this paper, the collapse behavior of PC structures with IBCCs under an internal column removal scenario is thoroughly assessed using experimental investigations and numerical analyses. Three PC subassemblages and one RC subassemblage are tested experimentally to provide experimental data for the calibration and validation of finite element (FE) models. The collapse behavior of full-span PC and RC subassemblages are next compared numerically under the internal column loss scenario, with an accompanying investigation on the influence of horizontal SSs. It is found that the PC subassemblages exhibit emulative collapse behavior as the RC subassemblage under internal column loss scenarios, provided that the horizontal SSs are located beyond the beam plastic region under the internal column loss scenario. To achieve the latter, a minimum distance of 0.15 L (L is clear beam span before column removal) is recommended for the positioning of horizontal SSs under the internal column loss scenario. Finally, it is shown that the fracture load and corresponding displacement can be enhanced with the incorporation of high ductility rebars.

Strengthening of reinforced concrete beams with insufficient lapped splice length of reinforcing bars

The insufficient lapped splice length of reinforcing bars due to the design or construction errors reduces both the flexural strength and ductility of Reinforced Concrete (RC) beams. The defected RC beams need to be strengthened to allow structures to be ductile and robust in their design life. This paper reports experimental and numerical investigations into the flexural behavior of RC beams having insufficient lapped splice length of reinforcing bars strengthened by various techniques. Eleven RC beams have been tested to examine the effects of strengthening techniques and anchorage lengths of the strengthening materials on the performance of the beams. The test program and results are described on RC beam specimens strengthened by using the externally bonded stainless-steel (EBSS) sheets, the near surface mounted (NSM) steel bars, and the external prestressing system. Finite Element (FE) models are developed using ABAQUS to simulate the responses of strengthened RC beams in which the lapped splice length of reinforcement is inadequate. A parametric study is conducted using the validated FE models to examine the effects of the length of EBSS sheets and steel anchor bolts at the ends on structural behavior. An analytical model is proposed for calculating the ultimate capacity of beams strengthened by NSM technique. Experimental results reveal that the proposed strengthening methods can significantly improve both the cracking and ultimate loads of the defected beams. The application of the external prestressing method results in the largest increase in the cracking and ultimate loads of the defected beams calculated as 222 % and 213 %, respectively compared to the defected control beam. The ultimate load of the defected beam strengthened with EBSS sheet, NSM steel bars, and prestressing system with a length of 100D increases by 50 %, 109 %, and 182 %, respectively. It is shown that the developed FE models can accurately predict the behavior of strengthened beams having inadequate lapped splice length of reinforcing bars. The parametric study demonstrates that strengthening the entire clear span of the beam B-ESS-65D with EBSS sheet increases its ultimate load by 207 %. The failure mode of strengthened beams is ductile bending without debonding. The proposed analytical model is shown to yield accurate calculations of the ultimate loads of strengthened RC beams.

Shear Behavior of Reactive Powder Concrete Ferrocement Beams with Light Weight Core Material

In this paper, the shear behavior of ferro-cement hollow beams is investigated experimentally and analytically. Ten reinforced concrete beams with cross-sectional dimensions of 100 × 200 × 1300 mm and a clear span of 1000 mm were cast and tested until failure under a two-point loading system. Ferrocement beams in this research contained either an autoclaved aerated lightweight brick core (AAC) or an extruded foam core (EFC) and were reinforced with either expanded metal mesh (EMM) or welded wire mesh (WWM). The structural behavior of the studied beams, including first crack, deflection, ultimate load, crack pattern, failure mode, and ductility index, was investigated. The experimental data were used to validate finite element models created with the ABAQUS finite element program. It can be concluded that the optimum performance of ferrocement beams can be achieved using beams with a second layer of expanded steel mesh as additional reinforcement, which led to an increase in the ultimate load and maximum deflection by 12.9% and 22.8%, respectively. Furthermore, the Numerical results agreed with the experimental results, where the ratio between the NLFE ultimate loads and the experimental ultimate loads varies between 1.02 and 1.07, with an average ratio of 1.04.

Effect of live loads on top slab of cast-in-place reinforced concrete box culverts

Reinforced concrete box culverts (RCBCs) designed according to old codes, using lighter truck weights (e.g., H15), may require posting when rated for current design and permit vehicles. When load ratings are calculated based on current AASHTO Specifications, they can be negatively affected by the conservative live-load attenuation through soil fill. This study evaluates the positive bending strains induced by live-load distribution through soil fill when load rating cast-in-place (CIP) RCBCs. Eighteen (18) single and multicell RCBCs in Kentucky were load tested and the effects of truck live loads analyzed. Fill heights, HF, varied from 0 m (0 ft) to 3.57 m (11.7 ft), clear cell spans, S, from 3.05 m (10.0 ft) to 6.71 m (22.0 ft), and culvert spans from 6.71 m (22.0 ft) to 18.59 m (61.0 ft). Field data were collected using strain gauges attached to the interior surfaces of culverts. Irrespective of how many cells the RCBCs had, strain variations with fill height in the top slabs were similar. At fill heights greater than 3.05 m (10.0 ft), maximum strains in the top slabs measured less than 10 microstrain, a value at which live-load effects are considered negligible. Combining live-load strains measured on the Kentucky culverts with ones from field tests in Missouri and Louisiana, a live-load tensile strain envelope is proposed to load rate the top slabs of RCBCs for positive bending when cell spans are less than 4.6 m (15.0 ft).

Flexural behavior and serviceability of steel fiber-reinforced lightweight aggregate concrete beams reinforced with high-strength steel bars

Six beams reinforced with HRB600 bars and one reinforced with HRB400 bars fabricated using steel fiber-reinforced lightweight aggregate concrete (SFLWAC) were tested under a four-point bending load to investigate the load-carrying capacity and service performance, with different reinforcement ratios, clear span lengths, concrete strengths, and reinforcement strengths. The test results showed that cracks ran through lightweight aggregates and developed rapidly without an aggregate interlocking mechanism, and the specimens eventually failed in the mode that the compressive concrete was crushed following longitudinal bars yielded, with 3 ∼ 4 major cracks. The specimens satisfied the allowable deflection and crack width required in the codes, with a ductility coefficient exceeding 4.5, and 1/150 of the span length was recommended to be the maximum deflection at the serviceability limit state. Generally, the increasing reinforcement ratio significantly improved the flexural strength and serviceability but reduced the ductility, the linear stiffness decreased with the growing span length, and the SFLWAC strength mainly affected the cracking moment and ductility. Replacing HRB400 bars with equal strength of HRB600 bars led to a substantial drop in serviceability, while an equal area of HRB600 bars improved the ultimate moment by 38.7 %. The calculation results indicated that by neglecting the residual tensile strength, fracture characteristics, and bond properties of SFLWAC, the prediction equations in the Chinese, American, and European codes underestimated the ultimate moment and overestimated the crack width, and the Chinese code yielded the conservative deflection prediction. The analytical flexural models for HRB600-reinforced SFLWAC beams were derived by incorporating the effects of steel fibers, lightweight aggregate concrete, and bond stress, exhibiting accurate predictions.

An experimental and numerical study on two-way RC slabs with openings strengthened by ferrocement technique

This study investigates the impact of creating a central square opening on reinforced concrete slabs and assesses the strengthening process using ferrocement layers. The investigated key parameters were the opening sizes, type, number, and extension length (outside the opening sides) of steel mesh layers used to strengthen the tested slabs. The experimental program included the preparation and testing of twelve two-way reinforced concrete slabs with identical dimensions, thickness, and reinforcement, but were different with respect to opening sizes and strengthening schemes. Four slabs acted as control specimens without strengthening; one was solid; the other three had different opening sizes; and the other eight slabs were strengthened using a ferrocement layer of 2 cm thickness applied on the bottom of the slab around the openings with various reinforcement schemes which included the number, type, and extension length (outside the opening) of steel mesh. All slabs were supported along the four sides with a clear span of 1 m in both directions and tested under four-point loading. The test results demonstrate that creating an opening in the slab decreases the ultimate load by 21.5 %, 31.9 %, and 40.7 % for opening dimensions (15, 25, and 35 cm), respectively. Using the ferrocement strengthening method helps to increase slabs’ flexural load-carrying capacities and reduce crack propagation from opening corners. The study found that strengthening specimens with opening sizes of 15, 25, and 35 cm increased their flexural load-carrying capacities by 26 %, 33 %, and 34 %, respectively. The expanded steel mesh type also resulted in a higher ultimate load by 6–7 % than the welded mesh type. When the length of the strengthening ferrocement layers was doubled, the ultimate load went up by 6–7 %. Increasing steel mesh layer numbers from 1 to 4 increased the ultimate load by 25 % to 40 % compared to the corresponding un-strengthened slab with an opening. The maximum load of a slab with an opening was achieved by applying a 2 cm thickness of ferrocement layer reinforced with expanded metal mesh, with extension lengths equal to the opening's length. The study utilizes commercial software ABAQUS for finite element analysis (FEA) to validate the experimental results, resulting in a great agreement between the analysis and the experimental findings.

Experimental and analytical study on enhancing flexural strength of RC beams using post‐ tensioned heavy‐duty metal straps wrapped around anchored steel plates

AbstractThis paper addresses the challenge of enhancing the bending capacity of beams through a cost‐effective and practical approach. Current methods are often expensive, brittle, time‐intensive, or massive. In response, an alternative method is proposed that involves the utilization of post‐tensioned heavy‐duty metal straps wrapped around steel plates anchored to the beams. To evaluate the effectiveness of the method, six large‐scale normal reinforced concrete beams were constructed with a width of 160 mm and a depth of 240 mm, and a clear span of 1900 mm. The testing parameters were the position of the steel plates along the length of the beam and the position of the metal straps along the height of the steel plates. Quantitative results demonstrate a significant enhancement in the load‐carrying capacity of the beams. Compared to the control specimen, the method led to a minimum increase of 40% of load carrying capacity and a maximum increase of 66%. Key influencing factors include the location of the metal straps on the steel plates (120 or 90 mm away from the bottom of the beam) and the position of the steel plates on the face of the beam (650 mm or 350 away from the edge of the beam). Notably, the load‐carrying capacity increases when the metal straps are positioned lower on the steel plates and the plates are placed further away from the center of the beam. Finally, analytical results obtained using VecTor2 software align well with experimental findings.

Experimental investigation on adaptive concrete slabs equipped with integrated fluidic actuators

One possible approach for saving structural mass and related emissions is to design adaptive load-bearing structures, i.e. actively reducing deformations under changing loads through actuation. This paper describes the application of a methodology based on influence matrices to identify a feasible actuator size for actuator placement in reinforced concrete slabs under multiple load cases. The design is implemented in a physical prototype comprising a concrete slab with a clear span of 2 m x 2 m, being equipped with fluidic actuators that are controlled via a cascade controller. Experimental tests show that the displacement response of the adaptive slab under twice the design load can be kept equal to that of the passive slab under the design load. Thus, proof of concept is provided that considerable material savings can be achieved by employing integrated fluidic actuators in two-way slabs.

Structural Behavior Castellated 2C Cold-Formed Steel Beams

This study's primary objective is to examine the structural behavior of using 2C-Cold produced. Section Castellated beams when subjected to monotonic load till failure. The experimental program testing. Seven Fabricated samples of castellated steel beams and one sample, which is a non-castellated steel beam (reference beam), were tested as supported beams under concentrated loads at two points over a clear span length (1730 mm). All castellated steel beams were similar in all properties and dimensions except the breadth of the upper and lower flanges. The current study considers the implications of modifying the width of the top and bottom flanges on how these beams behave. The findings showed that the ratio of the tested Castellated beams' ultimate load-carrying capacity to the non-castellated reference beam (R1) ranged from 99.3 to 117.2%, and the ratio of the tested beams' ultimate deflection to the same reference beam (R1) ranged from 72.6 to 103.2%. Increasing the breadth of the top and bottom flanges has a direct relationship with castellated beam stiffness and ultimate load. Finally, adjusting the flange width between the top and bottom flanges reduces castellated beam rigidity and ultimate load.

Paste, aggregate, or air? That is the question.

The Ambassador Bridge between Detroit, Michigan, and Windsor, Ontario, has served for almost 100 years as North America's busiest international border crossing. But in 2025, the Ambassador will be replaced by the new Gordie Howe International Bridge. The Gordie Howe is a cable-stayed bridge, with two massive 220 m tall concrete piers on opposite banks of the St. Claire River, a single clear span of 853 m, and 42 m of clearance over this busy waterway. To ensure durability in this harsh freeze-thaw environment, air-entrained concrete is specified throughout. And, to ensure the quality of air entrainment, the ASTM C 457 Procedure C, Contrast Enhanced Method is employed. While a similar automated microscopic approach has been in use for well over a decade according to EN 480-11 Determination of air void characteristics in hardened concrete, this is the first large-scale application of automated air void assessment in North American infrastructure. According to the ASTM Procedure C, the air void characteristics are determined through digital image processing, while the paste content may be determined by either mix design parameters, manual point count, or 'other means'. Of these three options, point counting is used for Gordie Howe; but in parallel, during each point count, the digital image coordinates and phase identifications for each evaluated stop are recorded. This allows for training of a neural network, for automated determination of paste content, as demonstrated here.

The Effect of Opening Size and Expansion Ratio on the Flexural Behavior of Hot Rolled Wide Flange Steel Beams with Expanded Web

In some design cases, such as in castellated beams, cellular beams, or steel beams with expanded web, it is advantageous to strengthen and enhance the performance of steel beams by increasing the web depth. However, expanding the web of a steel beam is a unique engineering strategy. This modification not only enhances its ability to bear heavy loads but also reduces any bending or flexing while enabling longer distances between supports. The expanded steel beams can be achieved by making a horizontal cutting in the steel beam web and then adding an increment plate (with the same web thickness), called spacer plate, between the two halves of the web sections, thus improving stiffness and strength. To evaluate the behavior of such beams, nine specimens of HEA steel beams with expanded web ratios of 150%, 200%, and 250%, and one specimen as a reference beam, were fabricated. The specimens were evaluated under two-point load over a clear span length of 280 cm. From the experimental work it was found that for steel beams with expanded web that have 18 openings with 80 mm, the beams with an expansion ratio of 150% had the best performance according to load-deflection behavior with a reduction in load capacity by only 11%. Additionally, the beams with expansion ratios of 200% and 250% had no economic viability according to the analysis of load-deflection behavior with a reduction in load capacity by 49% and 62%, compared with the solid expanded steel beam with the same expansion ratio. For the second type of steel beam with expanding web with 9 openings of 160 mm width, the beams with expansion ratios of 200% and 250% were observed to perform better than the first type with a reduction in load capacity by 28% and 50%. Using larger opening width and a smaller opening number is considered the best option for beams with expansion web ratios of 200% and 250%, while on the contrary, using smaller opening width and higher numbers seems to be a better option for beams with 150% expansion web ratio. Expanding the depth of a steel beam provides design flexibility, reduces deflections, and allows for longer spans. These benefits enhance material efficiency and open up new architectural possibilities.

Performance of doubly reinforced concrete beams with GFRP bars

Abstract The study focused on examining the behavior of six concrete beams that were reinforced with glass fiber-reinforced polymer (GFRP) bars to evaluate their performance in terms of their load-carrying capacity, deflection, and other mechanical properties. The experimental investigation would provide insights into the feasibility and effectiveness of GFRP bars as an alternative to traditional reinforcement materials like steel bars in concrete structures. The GFRP bars were used in both the longitudinal and transverse directions. Each beam in the study shared the following specifications: an overall length of 2,400 mm, a clear span of 2,100 mm, and a rectangular cross-section measuring 300 mm in width and 250 mm in depth. To apply loads for testing, two-point static loads were placed at the middle third of the beam’s span, creating a shear span of 700 mm in length. The beams were categorized into three groups depending on the GFRP longitudinal reinforcement ratio in the tension and compression zones of the section. GFRP bars with a diameter of 15 mm were employed as longitudinal reinforcement, while closed GFRP stirrups with a diameter of 8 mm at 100 mm were utilized as transverse reinforcement throughout the structural element. Test results have indicated that the ultimate load capacity of doubly GFRP-reinforced concrete beams varies compared to singly GFRP-reinforced beams. The range of variation observed is between an increase of 8% and a decrease of 4%. Accordingly, the contribution of the GFRP bars in the compression zone is insignificant and could be ignored in design calculations. It was observed that the loading level at which crack spacing stabilized ranged between 31.3 and 87% of the experimental failure load. It seems that the crack spacing decreased with the increase in the reinforcement ratio.

Quantifying the effect of end support restraints on vibration serviceability of mass timber floor systems: Testing

Design of mass timber floor systems is commonly governed by vibration serviceability due to high stiffness-to-weight ratio and low inherent damping of timber. Research and design practice have shown that static deflection under a concentrated load and fundamental natural frequency can be effective and robust indicators for vibration performance of mass timber floors. These design parameters are normally calculated by assuming simply supported conditions in existing design methods. However, such an assumption deviates from actual floor supports, especially in platform-framed buildings, and in-situ end support restraints have been widely recognized as a significant factor affecting the vibration performance. The purpose of the study is to quantify the influence of end support restraints on vibration serviceability of mass timber floors in platform construction through a comprehensive experimental program and analytical treatment. This paper is the first part and focus specifically on the experimental work on cross-laminated timber (CLT) panels. In particular, extensive laboratory tests have been conducted on different CLT floor panels with various end support restraints induced by top loads, self-tapping screws and steel angle brackets. The fundamental natural frequency and mid-span deflection under a concentrated load were measured for each end support configuration. The rotational restraint stiffness was determined by comparing results of restrained supports to those of simple supports and represented as end fixity factors. The analysis of test results shows that the CLT floor-to-wall connection exhibited inherent non-linear behaviour and such characteristic was more significant for higher top loads. Compared with screws and brackets, the top loads dominated the partially restrained effect but such dominance gradually diminished for lower-level top loads. In addition, support wall thickness notably impacts the support restraint. It was then suggested that the clear span could be used to determine deflection and frequency in the design, but further investigation is needed.

A possible underground roadway for transportation facilities in Kathmandu Valley: A racking deformation of underground rectangular structures

AbstractThe increasing number of private cars, public transportation vehicles, and pedestrians, as well as the absence of adequate space for these ground amenities, are one of the primary causes of traffic congestion and accidents in the Kathmandu Valley. Investigations have indicated that the Kathmandu Valley has the greatest traffic accidents despite the heavy presence of the government and its agencies there. Most teens and young adults suffer injuries while using motor vehicles. The study's primary objective is to foresee and prevent such complications by planning for sufficient subsurface infrastructure (a cut‐and‐cover rectangular tunnel) for the Kathmandu Valley's transportation network. The overlying pressure, lateral earth pressure, live load, uplift pressure, and live surcharge are some of the forces acting on the tunnel, creating unique stress and moment zones. The tunnel meets the following geometric requirements: (a) Each of the tunnel's two cells has a clear span of 10 m and a clear height of 5.5 m. The side walls, inner walls, top slab, and bottom slab are all 700 mm thick. Soil has built up to a height of 4 m over the tunnel's roof. The analytical method is used in the tunnel segment's analysis. Furthermore, the designed tunnel has been evaluated for stability, considering the deflection and shear resistance. The analysis indicates that the tunnel meets the stability requirements. This implies that the structure is capable of withstanding the applied forces without excessive deflection. Non‐linear dynamic time history analyses of the El Centro earthquake and the Gorkha earthquake were computed. From the El Centro earthquake, the maximum displacement was 23.63 mm at 10.59 s, and from the Gorkha earthquake, the maximum displacement was 16 mm at 0.19 s for the modeled structures.

Test study on performance of U80 standardized glass curtain wall system

In order to study the air infiltration performance, water penetration performance, structural performance under wind pressure and seismic inter-story drift performance of U80 standardized glass curtain wall system, one full size test specimen was designed according to the actual engineering situation. The test specimen was composed of six-unit curtain walls with exposed frames and six-unit curtain walls with concealed frames. According to the specification of United Stated, the various performance of the test specimen was investigated. The results show that the rate of air leakage of the specimen is within allowable values under design pressure. No water leakage is observed when the water penetration tests with static and dynamic pressure tests. During the structural performance tests at 100% design wind pressure, the deflections of framing members as well as glass panels are all within the allowable deflection limits. No breakage is observed under the 150% design wind pressure. Permanent deformations of framing members remain less than 0.1% of clear span. After 3 cycles of elastic and inelastic inter-story drift performance tests, no damage is observed. The U80 standardized glass curtain wall system has great air infiltration performance, water penetration performance, structural performance and seismic inter-story drift performance. And it can be used in the practical engineering.

Flexural Behavior of Rectangular Double Hollow Flange Cold-Formed Steel I-beam

This research experimentally investigates the flexural behavior of rectangular hollow flange cold-formed steel I-beam (RHFCFSIB) under two concentrated loads at the same distance from the support. All specimens were at a constant clear span of (L=1500mm), a constant beam specifications (t=4mm) web, flange thickness (h=300mm) for beam′s depth, and flange width of (bf=150mm). The connecting distance between the bolts, i.e., connects the web to the flanges, was (L/6), and eight stiffeners for each beam were placed under the load bearing points and at the support points on each side. The experimental program included assembling the parts to make beams and testing four specimens under two-point loads. The major parameters adopted in the current research included the flange depth, i.e., hf=30,60,90, and 120mm. The results showed that the beam with a flange depth of 30 mm had a higher ultimate load than other beams; however, it was the highest beam deflection. The beam with a flange depth of 120mm was the best section as a flexural member. The ultimate capacity of this beam increased by 15.34% and 6.4% compared to beams with flange depths of 60mm and 90mm and decreased by 12.9% compared to a beam with a flange depth of 30 mm. The maximum deflection at beam mid-span with a flange depth of 120 mm decreased by 53.8%, 44%, and 19.94% compared to beams with flange depths of 30 mm, 60mm, and 90mm, respectively. Therefore, the flange depth significantly influenced the flexural behavior by increasing the flange depth. Also, the ultimate capacity increased, and the deflection was reduced. The main conclusions drawn from the study were discussed and summarized. The research showed that the Hollow flanged sections gave the best results for flexural behavior.

Strength of Hybrid Steel-BFRP Reinforced Concrete Beams with Openings in the D-Region Strengthened Internally and Externally

The opened beams always confused the designers due to the guidelines missing. In this research, six hybrid beams reinforced with mixed steel and basalt fiber-reinforced polymer (BFRP) bars and having constant cross-sections of 150 mm × 300 mm and a clear span of 1800 mm were cast and tested under a four-point loading setup. Generally, five beams had symmetrical rectangular openings with dimensions of 150 mm × 250 mm located at a distance of 250 mm (equivalent to the beam effective depth) from the beam support, while an additional solid beam served as a control. The studied parameters included the effect of using internal reinforcement (steel or BFRP bars) provided adjacent to the opening sides or by incorporating an external BFRP sheet around the opening corners. Also, double enhancement with internal steel reinforcement bars together with external strengthening BFRP sheet was investigated. The relevant results showed that the opened beam without enhancement lost 75% of the maximum load compared with the solid beam. Placing internal steel or BFRP bars around the openings increased the maximum load by 62% and 60%, respectively, compared to the non-enhanced opened beams. Using an external BFRP sheet to strengthen the opening corners of the beam enhanced the maximum load by 76% compared with the non-enhanced opened beam. Consequently, by combining both the internal steel reinforcement and external BFRP sheet around the openings, the maximum load increased by 137% compared with the non-enhanced opened beam. Ultimately, a numerical analysis of the three-dimensional finite element model was performed to confirm the experimental findings, and the relevant results showed compatibility correlations with the experimental ones. Also, the effect of various parameters such as BFRP reinforcement ratio and number of BFRP sheet layers around the openings was investigated by adapting the validated numerical model.

Structural Performance of Reinforced Concrete Double Layer Bamboo Bubble Slab Under Uniformly Distributed Load

The architectural use areas in the structure are formed by reinforced concrete (RC) slabs, which transport vertical loads to the beams, columns, load-bearing walls, and shear walls. The slab is an important structural member of reinforced concrete building structures and concrete-intensive parts of structural members. . The slab deflects significantly when the load acting on the slab or the clear span between columns is large. As a result, the slab's thickness increases to accommodate the load received. Since this slab's self-weight increases as the thickness increases, the slabs get heavier and causes the slab unable to withstand the load and to produce cracks on the surface. At the turn of the twentieth and twenty-first centuries, the creation of the bubble deck slab became an innovation to replace conventional slab. This study used bamboo as the bubble material in reinforced concrete bubble slab. This study examined and assessed the mechanical properties and structural behaviour of bamboo as a bubble in supported reinforced concrete double-layer bamboo bubble slab under a uniformly distributed load. In this research, 500 mm x 1250 mm x 175 mm supported reinforced concrete slabs C25 (1 sample) and C30 (1 sample) with double layer (DL) bamboo bubble slabs were constructed. Both samples were compared with the control sample (CS) for each slab type. It was found that the maximum displacement occurred at the centre of the slab, with 6.45 mm for DL25 and 6.89 mm for DL30. According to stress-strain analysis, the double layer bamboo slab produced a lower stress value than the control sample. Since the values were smaller than 2, DL25 and DL30 slab performed better for the ductility factor than CS25 and CS30. As a result, the displacement, ductility and section capacity were improved by employing bamboo as a bubble material in a reinforced concrete slab.

Influence of the type of lintel and the method of covering the window opening on the compressive strength of walls made of AAC

AbstractThis article presents the results of tests on the compressive load capacity of AAC walls with a window opening with a clear span of 1550 mm. Different walls were tested in terms of confinement, concrete and the type of lintel. Standard lintels made of ordinary concrete and prefabricated AAC lintels were built in. Models of walls with additional cores placed along the vertical edges of window openings, in which lintel reinforcement was anchored, were also tested. During the study, apart from the load on the walls and deflection of the lintels, the morphology of cracking of the wall models around the lintel was also analyzed.

Behavior of high-strength concrete (HSC) box girders reinforced with GFRP bars, ties, and spirals under torsion

To date, the torsional behavior of high-strength concrete (HSC) box girders reinforced with glass fiber-reinforced polymer (GFRP) reinforcement has not been investigated. This study reports on the experimental results of HSC box girders reinforced with GFRP bars, ties, and spirals under pure torsion. Seven full-scale reinforced concrete (RC) box girders with a total length of 4,000 mm, width of 380 mm, height of 380 mm, and wall thickness of 100 mm were examined over a clear span of 2,000 mm. The test parameters included the type, configuration, and amount of the web reinforcement and the concrete type. All specimens have the same longitudinal reinforcement ratio. The test specimens comprised three box girders reinforced with GFRP bars and individual ties, three specimens reinforced with GFRP bars and continuous spirals, and one box girder entirely reinforced with steel reinforcement as a reference specimen. Two girders were fabricated with normal-strength concrete (NSC)—one reinforced transversally with GFRP spirals; the other reinforced with ties—to investigate the influence of concrete type on torsional behavior. The test findings indicate that, at the same web reinforcement ratio and reinforcement configuration, the HSC specimens achieved higher pre- and post-cracking torsional strength and stiffness than their counterpart NSC specimens. The continuous spiral configuration instead of individual ties improved the overall torsional performance of the tested box girders. Moreover, the stirrup's capacity strongly influenced the torsional strength of the GFRP- and steel-reinforced concrete box girders, but the stirrup stiffness did not affect the ultimate torque.