Composite Section Research Articles

Flexural strengthening of damaged steel beams with prestressed CFRP plates using a novel prestressing system

This study developed a novel prestressing system of the carbon fiber reinforced polymer (CFRP) plate to strengthen damaged steel beams, which reduced the operation space at the tensioning end, thereby extending the application range of prestressing system. Flexural tests were conducted to verify this system and investigate the effects of the adhesive layer, prestressing level, and CFRP plate area on the strengthening efficiency, and subsequently, a parametric analysis was carried out using finite element modeling to obtain more influencing rules of the unbonded CFRP plate-strengthened steel beams. The results indicated that satisfactory strengthening efficiency could be achieved by the novel prestressing system. The adhesive layer significantly affected the strain distributions of the steel–CFRP composite section, whereas it had a very slight effect on the flexural behavior of the steel beams, and the bonded and unbonded CFRP plates had a similar strengthening efficiency. Nonprestressed CFRP plate exhibited limited improvement in the flexural capacity and stiffness of the damaged steel beams under the normal service state; in contrast, the prestressed CFRP significantly increased the flexural behavior of the beams in the elastic and elastic–plastic stages owing to the high strength utilization of the CFRP plate. In addition, as the prestressing level increased, strengthening efficiency increased. Solely increasing the area or elastic modulus of the CFRP plate improved the strengthening efficiency slightly, whereas applying a prestress simultaneously clearly increases the strengthening efficiency. The strengthening efficiency increases with artificial notch depth.

Rectangular filled composite members made from high strength materials: Behavior and design of columns and beams

The AISC Specification limits the use of steel and concrete materials in filled composite members to concrete strength (fc′) less than or equal to 69 MPa and steel yield strength (Fy) less than or equal to 517 MPa. This paper presents the results of comprehensive analytical investigations conducted using benchmarked numerical models to evaluate the behavior of rectangular filled composite members made from one or both materials exceeding the AISC Specification strength limits. The numerical models are developed and analyzed using the displacement-based formulation of the fiber-based finite element in OpenSees. Prior research has developed effective (phenomenological) stress–strain curves for steel and concrete materials that implicitly account for the effects of steel yielding, local buckling, concrete cracking, crushing and confinement, and the interaction between the two materials in the composite cross-section. This paper first benchmarks the modeling approach and then uses the benchmarked model to conduct analytical parametric studies covering a wide range of parameters, including: member slenderness, section slenderness, section aspect ratio, steel yield stress and concrete compressive strength. The results from the parametric studies are used to evaluate behavior and develop new design equations based on nominal stress distributions over the composite section. The nominal steel stress in compression (Fcr) is expressed as a continuous function of the section slenderness and yield strength, thus eliminating the current AISC Specification’s need for section classification (compact, noncompact and slender). The new design equations are recommended for relaxing the material strength limitations in the next version of the AISC Specification.

Behavior of partial-length stiffened and full-length stiffened CFDST columns under axial load

Purpose Concrete-filled double skin tube (CFDST) columns are considered one of the most effective steel-concrete composite sections owing to the higher load carrying capacity as compared to its counterpart concrete-filled tube (CFT) columns. This paper aims to numerically investigate the performance of axially loaded, circular CFDST short columns, with the innovative strengthening technique of providing stiffeners in outer tubes. Circular steel hollow sections have been adopted for inner as well as outer tubes, while varying the length of rectangular steel stiffeners, fixed inside the outer tubes only, to check the effect of stiffeners in partially and full-length stiffened CFDST columns. Design/methodology/approach The behaviour of these CFDST columns is investigated numerically by using a verified finite element analysis (FEA) model from the ABAQUS. The behaviour of 20-unstiffened, 80-partially stiffened and 20-full-length stiffened CFDST columns is studied, while varying the strength of steel (fyo = 250–750 MPa) and concrete (30–90 MPa). Findings The FEA results are verified by comparing them with the previous test results. FEA study has exhibited that, there is a 7%–25% and 39%–49% increase in peak-loads in partially stiffened and full-length stiffened CFDST columns, respectively, compared to unstiffened CFDST columns. Originality/value Enhanced strength has been observed in partially stiffened and full-length stiffened CFDST columns as compared to unstiffened CFDST columns. Also, a significant effect of strength of concrete has not been observed as compared to the strength of steel.

Intermittently stiffened cold-formed steel GFRP composite lightweight built-up beams: Experimental investigation and performance assessment

Previous attempts to develop lightweight cold-formed steel (CFS) composite sections have successfully improved their buckling strengths but have been limited to unstiffened profiles only. This paper reports the results of an experimental program on the flexural behavior of newly developed CFSGFRP (Glass Fiber Reinforced Plastic) composite built-up open-section beams. In total, six large-scale specimens were tested under four-point loading with simply supported boundary conditions. To counter the inherent limitation of premature local buckling in the thin-walled CFS sections under compressive stresses, various combinations of intermittent stiffening and GFRP plank packing were adopted to improve the performance of the CFS GFRP lightweight composite beam specimens. The intermittent stiffening and GFRP plank packing were used judiciously in the compression flange and the web region of the specimens. A conventional open-section built-up beam was fabricated using two plain channels fastened through the web as a benchmark to evaluate the flexural performance of the composite beams. Furthermore, a hot-rolled steel beam with equivalent dimensions was also tested to give a broader comparison. The flexural performance of all the beams was assessed in terms of peak strength, initial stiffness, load–deformation​ response, failure modes and strength-to-weight parameter. The results confirmed the structural feasibility of adopting GFRP to form CFS lightweight built-up beams. The incorporation of GFRP planks significantly improved the flexural capacity by about 180% compared to the conventional CFS built-up beams. They also helped in attaining about 80% of the equivalent hot-rolled steel beam’s flexural strength, resulting in highly efficient built-up beams for practical applications.

Features of the Internal Force Factors Distribution in Reinforced Concrete Piles of Complex Cross Section under the Influence of a Transverse Load

Bar reinforced concrete structures, which include piles, in real working conditions perceive a whole range of internal force factors. Axial tension-compression forces, bending moments and shear forces are the most commonly perceived internal force factors. Of particular interest is the effect on the cross section of the shear force. If a complex curly shape is replaced by elementary form, then the calculation is not difficult. However, when calculating the composite cross section, there is no unambiguous solution. In accordance with the adopted regulatory documentation, it is necessary to accept only a main part, while discarding the surrounding areas. It is important to study the configuration of the shape of a complex section for the perception of a shear force. The purpose of the work was to refine the account of the entire complex section using numerical simulation by the finite element method, analytical calculations and small-scale experiments. Determination of further practical application of the obtained results on real structures was also the goal of the study. The parameters of the distribution of shear force between the main rib and flanges were obtained by numerical analysis and small-scale experiments. Numerical models of rectangular and tee cross sections beams have been developed. Analytical dependences were studied and full-scale tests of reinforced concrete beams of various sections were carried out. It has been established that when taking into account the work of the entire cross-section, the bearing capacity of concrete for the action of a shear force is 20% greater than when calculating only the main section without taking into account the shelves.

Springtime Southwest Cloud Bands in the Central Caribbean

Abstract Southwest cloud bands during spring (April and May) bring rains to central Caribbean islands at the end of the dry season. A cluster analysis of daily 500-hPa geopotential height fields for 1980–2021 identifies a low-west–high-east dipole pattern related to Pacific–North America response to El Niño–Southern Oscillation (ENSO) and springtime wet spells over the Dominican Republic and Puerto Rico. The regional dipole and local rain time series are ranked to identify the top 10 cases for analysis of meteorological conditions. Hovmöller plots of midlevel meridional wind and specific humidity during April 1983 and May 1986 wet spells reveal a standing Rossby wave train pattern that converges moisture onto the leading edge of a subtropical trough. Composite vertical sections during Caribbean Sea wet spells reveal lower easterly–upper westerly wind anomalies over South America associated with the equatorial Madden–Julian oscillation. Thunderstorm clusters within the southwesterly airflow induce multiday wet spells and flash floods. A second statistical method demonstrated how ENSO underpins Caribbean spring climate anomalies via tropical ocean–atmosphere Rossby wave coupling. Historical trends and long-range projections indicate that springtime tropical–midlatitude interactions may diminish due to an accelerating Hadley cell and retreating jet stream, leading to a delayed onset of the wet season across the Antilles Islands.

A NOVEL STRATEGY FOR SLIM‐FLOOR FIRE PROTECTION

AbstractThis paper presents a novel slim‐floor configuration which consist of an I‐section steel profile welded to a wider bottom steel plate with an insulation layer of 5mm thick placed in between the two. The insulation layer is made up of a flexible and non‐combustible material, which protects the I‐section profile from the temperature rise through its bottom surface. Besides, this insulation layer remains protected from external agents with no need of maintenance because it is placed in the cavity created on purpose between the bottom plate and the lower flange of the steel profile thank to the weld between them. This new slim‐floor configuration is currently right‐protected by the Spanish Office of Patents and Trademarks with the reference number P201930438 and has been tested in the Universitat Politècnica de Valencia testing facilities to assess its thermal behaviour in fire. Specifically, the specimen was tested using an electric furnace where the slim‐floor is placed at the top surface. Therefore, the composite beam is exposed to the heat source only from the bottom surface, as it is the case in real fire scenarios. Moreover, the experimental campaign includes also a common slim‐floor specimen, without the insulation layer, in order to compare their thermal behaviour. The steel parts used in all the test specimens were grade S355, having a nominal yield strength of 355 MPa, the nominal compressive strength (cylindrical) of the cast in‐situ concrete was 30 MPa and the precast concrete hollow core slabs were manufactured with 45 MPa nominal compressive strength (cylindrical). In turn, the embedded reinforcing bars were grade S500, with 500 MPa nominal yield strength. The first experimental results have shown that the temperature gap between the bottom steel plate and the lower flange of the steel profile can reach up to 200°C. This impressive thermal gap delays the temperature rise along the I‐section steel profile which produces a significant improvement on the composite section fire resistant time, up to 90 or 120 minutes. Additionally, it should be highlighted that the observed improvement on the cross‐section thermal behaviour has been achieved using a novel configuration which no need maintenance in contrast with the common external protection systems using intumescent coating or other fireproofing materials.

Https://journals.scholarpublishing.org/index.php/AIVP/issue/view/432

This research is focused on the structural setting and subsurface distribution of cretaceous facies in the Calabar Flank, Lower Benue Trough. The aim of this research is to compare the works of Nyong (1995), Reigers and Petters, (1997) in light of new available subsurface data. Materials used are data sets from three wells drilled at different periods within the same acreage (Wells A, B and C). Seismic data, well logs and mud log data have been used to analyze and study the subsurface geology of the study area. Well data from the three wells were viewed and matched with processed seismic data. A composite stratigraphic section produced show correlatable facies, their lateral extents and the subsurface facies distribution in the study area. Well A drilled, south central Calabar Flank encountered shale and sandstone, very thick shale unit with limestone overlying sandstone at the base. Well B also drilled south central Calabar Flank about 0.8km from Well A encountered the same sequence. Whereas Well C drilled about 4.7km from Well B encountered sandstone, shale, marlstone and limestone. This research shows that only well C encountered marlstone. Observations from the well sections, show the penetrated limestone unit appears disconnected, with very high resistive anomaly suggesting that the limestone reservoir penetrated by the three wells are not laterally continuous. These findings tend to modify the earlier published articles on the structural setting and subsurface distribution of Cretaceous sediments SW to NE of the Calabar Flank South Eastern Nigeria in terms of facies distribution, facies lateral extent and structural variability or changes.

Experimental Study on Steel Plate Shear Walls with Partially Encased Composite Columns Composed of Thin Steel Plate

The steel plate shear wall structure has excellent seismic performance, mainly consists of embedded steel plate, horizontal boundary elements (HBEs) and vertical boundary elements (VBEs). Under the action of additional bending moment, the VBEs of SPSW often produce the failure mode of “hourglass specimen”. As a solution, the SPSWs proposed in this paper adopts PEC columns, which are composed of concrete filled between flanges of thin-wall channel steel, and transverse steel bars welded between flanges to prevent it from buckling. A slow cyclic test was conducted on two specimens of 1/3-scaled prefabricated SPSWs with thin steel plate composite section PEC column. According to the validated finite element method, the parameters including the height-thickness ratio of filled steel plate, concrete strength grade, bolt spacing and axial compression ratio were also studied. The results show that the new structure has high bearing capacity and good ductility. In addition, the PEC column has enough stiffness to form a good anchoring effect for the inner steel plate. The inner steel plate fully yields after buckling and provides bearing capacity and energy consumption through the action of tension field. The peak load of specimens with concrete has a higher level approximately 18% than the no-concrete specimen. The height-thickness ratio has a great impact on the post buckling performance of SPSWs. With the increase of height-thickness ratio, the ultimate bearing capacity of the structure will increase by 10% – 30%. Moreover, to give full play to the outstanding performance of prefabricated SPSW with PEC column, the value range of bolt spacing is suggested to be in the range of 120 mm – 60 mm.

Multi-culm bamboo composites as sustainable materials for green constructions: section properties and column behavior

Round bamboo culms offer excellent sustainable materials for a green building construction. Round bamboo culms are tied or fastened into a multi-culm composite member to resist the heavier load. Circles externally touching each other can well model a multi-culm bamboo composite's section. This study aimed to obtain formulas for drawing a cross-section of a multi-culm bamboo composite, calculating its section properties, and then embedding them into a graphing calculator and spreadsheet. As many as nine full-sized single and multi-culm bamboo composite columns were tested in the laboratory to resist the buckling load until the failure occurred. The column acting as the sum of some individual culms capacity was considered. In addition, the embedded equations analyzed the multi-culm column working in unity as a composite. This study found that the multi-culm columns tend to inhibit the combination (pseudo-composite) behavior rather than acting as a perfect composite column or the sum of individual culm's capacities. A perfect composite columns approach resulted overestimated value of the multi-culm column's critical buckling load; on the other hand, the sum of individual culm's capacity approach approximated underestimated value. The weighted average approach with a weight coefficient of k = 1 explains the empirical critical buckling load-bearing capacity's variance very well.

Influence of Composite Skin on the Energy Absorption Characteristics of an Aircraft Fuselage

In aviation history, accidents during landing are more frequent compared to other phases of flight and in most cases the aircraft is forced to make an emergency belly landing when landing gear malfunctions. This study aims to analyse the energy absorption of a typical composite aircraft fuselage section under such crash belly landing. A finite element model of this composite fuselage section was created and analyzed using LS-Dyna finite element software and the effects of different composite materials on the energy absorption of fuselage section were studied. Four different composite materials that are commonly used in aerospace application were selected for the purpose of the present study namely glass/epoxy, graphite/epoxy, Kevlar/epoxy, and boron/epoxy. An impact velocity of 7 m/s against rigid ground was considered. Results showed that frames and skin contribute the most in energy absorption while the passenger floor and strut contribute the least. Moreover, it was found that fuselage skin made of glass/epoxy absorbed more energy compared to other materials and it had the highest specific energy absorption.

Stratigraphy of the Cretaceous/Paleogene (K/Pg) boundary at the Global Stratotype Section and Point (GSSP) in El Kef, Tunisia: New insights from the El Kef Coring Project

The Cretaceous/Paleogene (K/Pg) boundary is marked by one of the largest mass extinctions in Earth’s history, with geological evidence for this event being expressed in hundreds of locations worldwide. An extensively studied section located near El Kef, northwestern Tunisia, is characterized by the classic iridium-rich K/Pg boundary layer, abundant and well-preserved microfossils, and apparently continuous sedimentation throughout the early Danian with no previously described structural complication. These features led to its designation in 1991 as the Global Stratigraphic Section and Point (GSSP) for the base of the Danian (i.e., the K/Pg boundary). However, the outcrop section has become weathered, and the “golden spike” marking the GSSP is difficult to locate. Therefore, the El Kef Coring Project aimed to provide a continuous record of unweathered sediments across the K/Pg transition in cores recovered from five rotary-drilled holes located close to the El Kef GSSP. Here, we present new, high-resolution lithologic, biostratigraphic, and geochemical data from these cores. The recovered stratigraphic successions of each hole (all drilled within ∼75 m of one another) are unexpectedly different, and we identified a formerly unknown unconformity within planktic foraminiferal biozone P1b. Our results provide evidence that sedimentation at El Kef was not as continuous or free from structural complication as previously thought. Despite these challenges, we present a new composite section from the five El Kef holes and an age model correlated to the orbitally tuned record at Walvis Ridge, South Atlantic Ocean, which is critical in placing the paleoenvironmental and paleoecological records from El Kef in a global context.

Strengthening and toughening of Cu matrix composites reinforced by metallic glass particles with variable size

Metallic glass particle reinforced CuCrZr composites with excellent mechanical and electrical properties are manufactured by ball milling and spark plasma sintering. The effect of reinforcement size on the microstructure and properties of composites is investigated. As the size of metallic glass particles decreases, the strength and toughness of the composites are jointly increased. Quantitative results of the strengthening mechanism show that the strength is mainly provided by grain boundaries and metallic glass particles, with the fine and dispersed metallic glass reinforcements contributing more to the strength. Furthermore, crack extension behavior under uniaxial compression is observed for composite sections. The results indicate that cracks sprout and expand along the interface, and the interface bonding modified by the ball milling (BM) process can effectively inhibit the crack merging process. In particular, the crack extension rate corresponds to the plasticity of the particle-reinforced composite as determined by the interfacial properties, particle size and distribution of the reinforcement.

Exploring the potential of the critical shear crack theory for reinforced and post-tensioned glass beams: Initial analysis and experiments

In the evolution of structural glass beam elements, the requirements for post-fracture load bearing capacity and safe failure behaviour have led to the development of reinforced and post-tensioned beams. Maximum bending capacity in the post-fracture state is normally associated with extensive yielding of the reinforcement, providing a safe failure mechanism through apparent ductility of the composite beam section. This can be achieved as long as the propagation of primary flexural cracks does not compromise the transfer of shear from the load points to the supports. Although shear failure is typically not critical for the ultimate limit state design of ’normal’ unreinforced glass beams, it may govern the load-bearing and deformation capacity in the post-fracture state for reinforced and post-tensioned glass beams. This paper presents exploratory experiments and initial analysis of the shear failure phenomenon in the post-fracture state of reinforced and post-tensioned glass beams. Potential shear transfer mechanisms are identified based on the critical shear crack theory developed for reinforced concrete members and applied in the analysis of shear failures observed in four-point bending tests of post-tensioned glass beams. The behaviour of fractured laminated glass under mixed-mode (tension+shear) loading is explored on a limited set of small-scale double-notched glass specimens, demonstrating the feasibility of the applied test methodology. Preliminary findings of the present study may serve as a basis for further investigations of shear resistance of glass beams. Typical shear failure kinematics and suitable constitutive laws of the applied materials need further investigation in order to provide design recommendations for the prediction of shear resistance of reinforced and post-tensioned glass beams.

Compressive performance of an innovative tall pier with composite box section

To improve the seismic performance of tall-pier bridges, an innovative tall pier with a composite box section, composed of four-limb concrete-filled steel tube (CFST) columns and low-yield-strength (LYS) steel plates, was proposed based on the principle of capacity design and the replaceable fuse concept. Both axial and eccentric compression tests were conducted on a series of specimens to study the compressive performance of the composite tall pier. Parametric analysis was performed to investigate the effects of load eccentricity, slenderness ratio, thickness, and yield strength of the LYS steel plates on the compressive capacity using validated finite element (FE) models. The main results indicate that the composite tall pier fails with global bending deformation and elastoplastic instability under axial or eccentric compression. The compressive capacity and initial stiffness of the composite tall pier decrease significantly with an increase in eccentricity or slenderness ratio, and the influences of eccentricity and slenderness ratio are essentially independent. Additionally, the increase in the thickness of the steel plates enhanced the flexural stiffness and compressive capacity, and reduced the uneven loading distribution for the pier. Under axial compression, the pier can be simplified as a CFST lattice column connected by steel beams and LYS steel plates. Finally, practical formulas for the compressive capacity are proposed considering the connection and restraint effects of the LYS steel plates on the CFST columns, which can be used to predict the compressive capacity of the novel composite tall pier.

Influence of the bevel and steeple triggers on crashworthiness of carbon fiber-reinforced composite channel section structure

To induce the progressive crushing of composite channel section structure (CCSS), the bevel and steeple trigger are proposed and designed. A nonlinear damage model considering both damage initiation and evolution of intra-ply and inter-ply is developed. The damage initiation and stiffness degradation processes of intra-ply are predicted by the maximum stress criterion and an exponential evolution law, respectively. The adhesion behavior between adjacent plies is modeled following the surface-based cohesive contact method, and the delamination failure behaviors of inter-ply are predicted using the traction-separation model. The effects of different configurations of bevel and steeple trigger on the energy absorption characteristics of CCSSs subjected to quasi-static axial loading are compared and analyzed. The results show the initial peak load of CCSS using the bevel and steeple trigger has a negative correlation function with the bevel angle. The steeple trigger can induce progressive crushing of the structure and significantly enhance the specific energy absorption (SEA).

INVESTIGATION ON CONCRETE FILLED SKINNED BEAMS

Steel-Concrete-Steel Sandwich (SCSS) beam is a relatively new and innovated form of construction consisting of a layer of concrete, sandwiched between two relatively thin plates of steel which are connected to the concrete by shear connectors. In this project we investigated the difference between conventional Beam strength & concrete filled skinned beams strength. These skinned beams consist 1.5mm thick Steel plate and 1m in length, welded with 4 nos of 8mm diameter bar using shear connector consists of 12mm dia bar placed at spacing of 150mm in two rows of longitudinal section. It is a composite sandwich concrete section. Key Words: 1.5mm Steel plate 1m, 4 nos of 8mm diameter, M25 concrete.

Multi-proxy record of ocean-climate variability during the last two millennia on the Mackenzie Shelf, Beaufort Sea

A 2,000 year-long oceanographic history, in sub-centennial resolution, from a Canadian Beaufort Sea continental shelf site (60meters water depth) near the Mackenzie River outlet is reconstructed from ostracode and foraminifera faunal assemblages, shell stable isotopes (delta 18O, delta 13C) and sediment biogenic silica. The chronology of three sediment cores making up the composite section was established using 137Cs and 210Pb dating for the most recent 150 years and combined with linear interpolation of radiocarbon dates from bivalve shells and foraminifera tests.Continuous centimeter-sampling of the multicore and high-resolution sampling of a gravity and piston core yielded a time-averaged faunal record of every approximately 40 years from 0 to 1850 CE and every approximately 24 years from 1850 to 2013 CE. Proxy records were consistent with temperature oscillations and related changes in organic carbon cycling associated with the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). Abundance changes in dominant microfossil species, such as the ostracode Paracyprideis pseudopunctillata and agglutinated foraminifers Spiroplectammina biformis and S. earlandi, are used as indicators of less saline, and possibly corrosive/turbid bottom conditions associated with the MCA (approximately 800 to 1200 CE) and the most recent approximately 60 years (1950–2013). During these periods, pronounced fluctuations in these species suggest that prolonged seasonal sea-ice melting, changes in riverine inputs and sediment dynamics affected the benthic environment. Taxa analyzed for stable oxygen isotope composition of carbonates show the lowest delta 18O values during intervals within the MCA and the highest during the late LIA, which is consistent with a 1 degree to 2 degree C cooling of bottom waters. Faunal and isotopic changes during the cooler LIA (1300 to 1850 CE) are most apparent at approximately 1500 to 1850 CE and are particularly pronounced during 1850 to approximately 1900 CE, with an approximate 0.5 per mil increase in delta 18O values of carbonates from median values in the analyzed taxa. This very cold 50-year period suggests that enhanced summer sea ice suppressed productivity,which is indicated by low sediment biogenic silica values and lower delta 13C values in analyzed species. From 1900CE to present, declines in calcareous faunal assemblages and changes in dominant species (Cassidulina reniforme and P. pseudopunctillata) are associated with less hospitable bottom waters, indicated by a peak in agglutinated foraminifera from 1950 to 1990 CE.

Numerical modeling of inverted-U-shaped connectors to enhance the performance of composite beams

Steel and concrete are the most essential and frequently encountered building materials. These materials are used in combined structural systems, such as concrete cores surrounded by steel pipes, as well as composite structures with steel and concrete components. In numerous countries, the combination of concrete cores, steel frames, and composite slab construction has become the typical construction approach for multistory commercial buildings. The shear stud connector is one of the elements used in the construction of composite sections. The use of inverted-U-shaped reinforcement experimentally and numerically significantly improves punching shear resistance for post-tensioned slabs compared with slabs that use stud connectors. Other experimental and numerical studies using inverted-U-shaped reinforcement in post-tensioned beams indicate an enhancement in their shear strength. Recently, an experimental investigation was performed on composite beams to inspect the effect of mild and rigid shear stud connectors. The experimental and numerical results for the composite beams showed good correlation. The goal of this study was to numerically model the capacity and deformation of composite beams with inverted-U-shaped connectors of varying configuration and mechanical properties and compare the beam performance with composite beams using shear stud connectors.

Enhancement of the behaviour of reinforced concrete dapped end beams including single-pocket loaded by a vertical concentrated force

In precast building construction, some beams are designed to support one or several concentrated loads resulting from the reactions of the attached cross beams. Consequently, the pocket beams without or with dapped ends may represent one of the innovative solutions to constitute the joints between the two attached members. In the present research work, the behaviour of dapped end beams that included rectangular opening loaded with in-plane force, have been investigated. Several detailing have been proposed, in addition the vertical stirrups, to improve the strength of the opening region including the use of steel fibre concrete (SFC),Configuration of the inclined crossed bars, jacketing with steel plates and the composite section technique with two arrangements of the reinforcement of the dapped end . Ten specimens have been tested under gradually increased vertical static loading. The tested specimens are categorized into two sets based on the configuration of dapped end reinforcement. Two variable have been considered which are the strengthening configuration of the opening region and the configuration of the dapped end reinforcement. The response has been discussed in terms several indicators including, the cracking and failure loads, maximum deflection, mode of failure, load-deflection curves, crack patterns, crack width, to recognize the optimum strengthening proposal of the opening. Results revealed that using the inclined steel bars (modified arrangement) yield better response than the conventional (standard) reinforcement (vertical stirrups) within the dapped end. For beams with pockets strengthened with crossed inclined bars, failure load enhanced in range of (8.5-11%) whereas the enhancement was in ranged in (8-10%) for the steel SFC method. Moreover, an improvement by about (11-13%) in load capacity increased when the jacketing with steel plates was applied. The maximum improvement was obtained when using the embedded rolled section within the opening with values of (21-23%).