Horizontal Shear Strength Research Articles

Horizontal shear behavior of self-compacting lightweight concrete composite beams with dry joints and unbonded reinforcements

This study aims to investigate the horizontal shear behavior of self-compacting lightweight concrete (SCLC) composite beams with dry joints and unbonded transverse reinforcement. For this, the experimental program included different concrete types, joints configurations, and the use of unbonded high-strength bars with varying levels of prestressing and transverse reinforcement ratios in composite beams. Two precast beams were fabricated using a match-cast method and integrated horizontally to form composite beams, utilizing unbonded transverse reinforcements. The composite beams incorporating lightweight aggregates (LWA) instead of normal weight aggregates (NWA) exhibited a decreased ultimate shear strength of 19.5 %; however, the addition of steel fibers into the mixtures mitigated this decrease, resulting in a 22.8 % increase in strength compared to mixture without steel fibers. The vertical prestressing level significantly influenced the horizontal shear behavior and failure mode of composite beams, with adequately prestressed composite beams exhibiting similar ductile behaviors to the monolithic beam. Composite beams with keyed joints exhibited higher horizontal shear strength, up to 65.3 % more than the beam with flat joint, attributed to the interlock provided by the shear keys. Increased slip between two precast beams activated the dowel action of unbonded reinforcements, effectively resisting horizontal shear. Predictions of the horizontal shear strength, as per current codes, were compared to the experimental results. The results indicate that the design approach in Eurocode 2 provides reasonable estimations of the strengths of composite beams with dry joints and unbonded reinforcements.

Geotechnical characteristics and seismic stability evaluation of pumice-fall deposits soil on collapse slope by the 2018 Hokkaido eastern Iburi earthquake

The September 6, 2018, earthquake in the eastern part of Hokkaido, Japan, caused extensive slope failures in Atsuma-town, Hokkaido, Japan. In this study, the authors performed in situ investigations, including trenching and portable dynamic cone penetration tests, on weathered fallen pumice sediments, which are one of the causes of the slope failures. In addition, we performed direct box shear tests on undisturbed samples collected from an undisturbed area under various shear conditions to characterize mechanical properties of the soil. The parameters obtained from the mechanical tests were used to evaluate slope stability under normal and seismic conditions with an infinite-length slope model. The results showed that the slopes where seismic failures occurred had a fragile layer from the surface to a depth of approximately 1.5 m, which generally corresponded to the depth of failure. Weathered pumice deposits with extremely high-water content existed at the boundary between the weak layer and the basement layer, and their shear strength was velocity dependent. It has been shown that an infinite-length slope stability analysis can be performed by using mechanical parameters for which velocity dependence of horizontal acceleration and shear strength due to seismic motion are accounted for.

Durability of GFRP and CFRP Bars in the Pore Solution of Calcium Sulfoaluminate Cement Concrete Made with Fresh or Seawater.

Calcium sulfoaluminate cement concrete (CSAC) reinforced by fiber-reinforced polymer (FRP) bars, termed bars for brevity, is a good alternative to steel-reinforced concrete in marine environments due to the corrosion resistance of FRP and the lower pH of CSAC. For the first time, multi-mechanical tests are conducted to compare the durability of glass FRP (GFRP) to that of carbon FRP (CFRP) after exposure to CSAC pore solution. The bars were immersed in a simulated pore solution of CSAC made with either fresh water and river sand or with seawater and sea sand. Solution temperature was held constant at 30 °C, 45 °C or 60 °C for 30, 60, 90 and 180 days of immersion. Tensile, horizontal and transverse shear tests, as well as detailed microstructural analyses, were conducted to determine the level and mechanisms of degradation for each type of bar. Sea salt increases the degradation of both bars, but it degrades GFRP more than CFRP. The bars' retained tensile strength is a reliable indicator of their durability, while their post-exposure horizontal and transverse shear strengths are found inconsistent and counter intuitive. In the GFRP, the fiber, the epoxy matrix and their interface suffered damage, but in the CFRP, the carbon fiber was not damaged. Under the test conditions in this study, the maximum reduction in the tensile strength of the GFRP was 56.9% while that of CFRP was 15.1%. Based on the relevant ASTM standard, the CFRP bar satisfies the alkaline resistance requirement of the standard in the CSAC pore solution with and without salt, whereas the GFRP bar does not meet the same requirement in the above pore solution with salt.

Interface horizontal shear strength requirement in Ultra-thin whitetopping (UTW) pavement.

Ultra-thin whitetopping (UTW) is a thin (5-10 cm) layer of concrete overlaying over an existing asphalt pavement. This concrete layer is bonded on the asphalt surface. Although UTW has been successful in strengthening asphalt pavement, in some cases, the composite pavement may debond at the interface under the concrete slab due to high shear stress. This paper aims to determine the interface shear strength required for UTW pavement systems using theoretical methods and calibrated numerical models (FEMs). The study analysed 432 pavement scenarios with different slab sizes, thicknesses, and material properties. The results show that higher shear stress occurs when the asphalt modulus is stiffer. The size of the slab, the modulus of the supporting layer, and the asphalt thickness have only a minor effect on the shear stress value. However, the thickness of the concrete slab significantly affects the maximum shear stress in the UTW, with an increase of up to 36.6% when reducing the slab thickness from 100mm to 50 mm. The FEM calculations can be used to determine the required interface horizontal shear strength for UTW.

Effect of Furfurylation on Bamboo-Scrimber Composites

Bamboo is a material with excellent development prospects. It is increasingly used in furniture, decoration, building, and bridge construction. In this study, Furfurylated bamboo bundles and phenol-formaldehyde resin were used to make bamboo-scrimber composites (BSCs) via molding-recombination and hot-pressing processes. The effects of the impregnation mode, furfuryl-alcohol concentration, and curing temperature on the various physical-mechanical properties and durability of the composites were evaluated. Scanning-electron microscopy (SEM) was used to observe the microstructural differences. Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were employed to investigate changes in the chemical constituents. The heat resistance was also investigated using thermogravimetric analysis. The results showed that the density of the furfurylated BSC increased by up to 22% compared with that of the BSC-C with the same paving mode. The furfurylated BSCs had lower moisture contents: the average moisture content of the furfurylated BSCs was 25~50% lower than that of the BSC-C. In addition, the furfurylated BSCs showed better dimensional stability and durability, since the decay-resistance grade of the BSCs was raised from decay resistance (class II) to strong decay resistance (class I). In terms of the mechanical properties, the furfurylation had a slight negative effect on the mechanical strength of the BSCs, and the modulus of rupture (MOR) and horizontal shear strength (HSS) of the BSCs were increased to a certain extent under most of the treatment conditions. In particular, the highest HSS for indoor use and MOR of the furfurylated BSCs increased by 21% and 9% compared with those of the untreated BSCs, respectively. The SEM results indicated that the FA resin effectively filled in the bamboo-cell cavities and vessels, and the modified bamboo-parenchyma cells were compressed more tightly and evenly. The FTIR and XPS spectroscopy showed that the hydroxyl group of carboxylic acid of the bamboo-cell-wall component reacted with that of the furan ring, and the cellulose and hemicellulose underwent acid hydrolysis to a certain extent after the furfurylation. Overall, the present study highlights the potential of furfurylation as a modification method to enhance BSC products. Further research should focus on improving the ability of furfurylated BSCs to prevent the growth of Botryodiplodia theobromae. Additionally, the influence of furfuryl-alcohol resin on the bonding strengths of PF adhesives should be further clarified.

Residual flexural behaviour comparison between composite and monolithic beams after fire exposure

Fourteen T-shaped composite beams and seven T-shaped monolithic beams were tested after fire exposure. To investigate their distinct residual flexural behaviour, the beams, which had different load ratios and thicknesses of precast slabs, were exposed to specific fire exposure times (60, 90, and 120 min) in a fire furnace and loaded to failure after natural cooling. The results showed that the residual flexural capacity of the composite beams was generally lower than that of monolithic beams. The fire exposure time was found to dominantly influence the residual flexural capacity of the composite beams. Increasing the thickness of the precast slabs can slightly enhance the residual strength of the composite beams. However, the horizontal cracks at the interface between the precast and cast-in-place concrete slabs of the composite beams reduced the horizontal shear strength and further increased the horizontal slip along this interface. Accordingly, a finite element model of the composite beams was proposed. A three-dimensional spring element was introduced into the model to consider the effect of slip at the concrete–concrete interface. To predict the residual flexural capacity of the composite beams, based on the 500°C-isotherm method, three modified equations suitable for the Chinese, American, and European codes were proposed. In comparing the test values, the modified equation applicable to the European code is recommended for subsequent predictions.

Lateral crural setback: an analysis on tip rotation

<p class="abstract"><strong>Background: </strong>Increasing nasal tip rotation is a common objective during rhinoplasty. When ptosis is either totally or partially the result of an excessive lateral crura length, strength, or position, various techniques have been used to shorten the lateral crura in order to reduce its relative inferior ptotic force. Techniques that involve division or amputation of the cartilage have been shown to be effective, but may sometimes weaken the cartilage’s shear and horizontal load strength, thus increasing the chances of unwanted sequalae in alar and/or tip contour. We presented our lateral crural setback technique as another option to allow the tip to rotate while maintaining the lateral architectural structure, end to end continuity, and horizontal load and shear strength.</p><p class="abstract"><strong>Methods:</strong> Retrospective review of 20 patients undergoing cosmetic rhinoplasty who had a lateral crural setback cartilage repositioning maneuver. The primary outcomes measured after one year of follow-up were nasal tip rotation and projection. Nasal tip rotation was assessed by measures of the nasolabial angle using three different methods.</p><p class="abstract"><strong>Results: </strong>There was a statistically significant increase in nasolabial angle using all 3 methods for measuring nasal tip rotation. The average increase in nasal tip rotation for all methods was 10.7° (p<0.0001). There was a statiscically significant decrease in tip projection. No alar distortion or complications were noted.</p><p class="abstract"><strong>Conclusions:</strong> The lateral crural setback technique can be used to increase nasal tip rotation while preserving the integrity of the lateral crura. No alar distortion or complications were noted from this procedure. </p>

"Impact of shear connectors on composite action in full-depth precast concrete bridge systems"

This theoretical research used the finite element method to model full-depth precast concrete deck slabs. It examined the effects of pocket spacing and number of shear studs per pocket. Results indicat­ed that horizontal shear strength increases with the number of pockets in both supported and continu­ous-span models. Load–deflection curves and slippage values were recorded and compared with experimental tests, confirming that pocket spacing is an important factor and that the number of studs and their config­uration affects the load for slippage induction. The parametric study evaluated effects of shear connector sizes and various numbers of shear studs for distances of 24 and 48 in. (609.6 and 1219.2 mm) between shear pockets for simply supported bridges; however, there is a need for experimental evaluation of shear connector performance on design.

Durability assessment of GFRP rebars in marine environments

Technologies developed over the last two decades have facilitated the use of glass fiber reinforced polymer (GFRP) bars as internal reinforcement for concrete structures, specially in coastal environments, mainly due to their corrosion resistance. To-date, most durability studies have focused on a single mechanical parameter (tensile strength) and a single aging environment (exposure to high alkalinity). However, knowledge gaps exists in understanding how other mechanical parameters and relevant conditioning environments may affect the durability of GFRP bars. To this end, this study assesses the durability for different physio-mechanical properties of GFRP rebars, post exposure to accelerated conditioning in seawater.Six different GFRP rebar types were submerged in seawater tanks, at various temperatures (23°C, 40°C and 60°C) for different time periods (60, 120, 210 and 365 days). In total six different physio-mechanical properties were assessed, including: tensile strength, E-modulus, transverse and horizontal shear strength, micro-structural composition and lastly, bond strength. It was inferred that rebars with high moisture absorption resulted in poor durability, in that it affected mainly the tensile strength. Based on the Arrhenius model, at 23°C all the rebars that met the acceptance criteria by ASTM D7957 are expected to retain 85% of the tensile strength capacity.

Influence of Four Ageing Methods on the Mechanical Properties of Bamboo Scrimber

In this study, the six-cycle accelerated ageing method (method I), the 6 h boiling-freezing-drying method (method II), the wet circulation method (method III), and the boiling-testing method (method IV), which are accelerated ageing testing methods, were used to study the ageing resistance of bamboo scrimber. Changes in the nail-holding power of the plane, the side, and the end face of untreated/treated bamboo scrimber were analyzed systematically, including other changes in mechanical properties, such as the horizontal shear strength, the modulus of rupture (MOR), and the modulus of elasticity (MOE) along the smooth grain, etc. The results show that all mechanical properties decreased after treatment with the four accelerated ageing testing methods: the nail-holding power decreased by 4%~42% on the plane, 8%~40% on the side, and 5%~66% on the end face. The horizontal shear strength decreased by 3.1%~16.7%, the MOR decreased by 15%~27.2%, and the MOE decreased by 2.6%~12.8%. The nail-holding power of the three sides and the MOR were the most affected properties after treatment. So, the nail-holding power and the MOR can be chosen as important indices to evaluate bamboo scrimber’s weather resistance. For the four accelerated ageing testing methods, the degree of influence on the nail-holding power was in this sequence: method I > method III > method IV > method II. However, after comprehensive consideration, the degree of influence on the mechanical properties was in this sequence: method I > method IV > method III > method II.

Comparative Study of Structural Behavior for Asymmetrical Castellated (Concavely - Curved Soffit) Steel Beams with Different Strengthening Techniques

The Asymmetrical Castellated concavely – curved soffit Steel Beams with RPC and Lacing Reinforcement improves compactness and local buckling (web and flange local buckling), vertical shear strength at gross section (web crippling and web yielding at the fillet), and net section ( net vertical shear strength proportioned between the top and bottom tees relative to their areas (Yielding)), horizontal shear strength in web post (Yielding), web post-buckling strength, overall beam flexure strength, tee Vierendeel bending moment and lateral-torsional buckling, as a result of steel section encasement. This study presents two concentrated loads test results for seven specimens Asymmetrical Castellated concavely – curved soffit Steel Beams section encasement by Reactive powder concrete (RPC) with laced reinforcement. The encasement of the Asymmetrical Castellated concavely – curved soffit Steel Beams consists of, flanges unstiffened element height was filled with RPC for each side, and laced reinforced which are used inclined continuous reinforcement of two layers on each side of the Asymmetrical Castellated concavely – curved soffit Steel Beams web. The inclination angle of lacing reinforcement concerning the longitudinal axis is 45. Seven specimens with seven different configurations will be prepared and tested under two concentrated loads at the mid-third of the beam span. The tested specimen's properties are: unconfined Asymmetrical Castellated Steel Beams (Reference1), second model; Asymmetrical Castellated concavely – curved soffit Steel Beams (web and flange) confined with (RPC) only, third model; Asymmetrical Castellated concavely – curved soffit Steel Beams (web and flange) confined with (RPC) and laced reinforcement, fourth model; is same as the third model but it has one web opening with increase the depth of web post by 10 %, 20%, and 30 % as a gap between top and bottom parts of Asymmetrical Castellated concavely – curved soffit Steel Beams respectively. The results that have been obtained from the experimental part and the numerical analysis results by ABAQUS demonstrated that the increase of the gap leads to an increase in the load against the deflection curve. Sample CB8 with 122 mm gap has gained the highest load against deflection when compared with either reference sample without gap and other samples with 65 mm and 105 mm gap for concavely–curved soffit Steel Beams.

Bond durability of BFRP bars embedded in concrete with fly ash in aggressive environments

Fiber-reinforced polymer (FRP) bars are an environmentally friendly alternative to steel and are considered ideal substitutes for steel reinforcement in marine concrete structures due to their excellent resistance to chloride ions and mechanical properties. However, the strong alkaline environment in concrete results in the degradation of FRP bars, and the degradation of FRP bars is detrimental to the long-term performance of these structures due to the decrease in interfacial bonding. This study aims to investigate the bond durability of basalt FRP (BFRP) bar and concrete with or without fly ash in corrosion environments by pull-out tests. The laboratory-accelerated aging environments are an alkaline solution (pH 12.8 ± 0.2) and simulated seawater, and the immersion temperatures are set at room temperature (~26 °C), 40 °C, and 60 °C. Furthermore, the mechanical properties of the BFRP bars are also determined under the same conditions. Results indicate that the mechanical properties of the BFRP bars and the bond strength decrease as the immersion time increases. The addition of fly ash in concrete can improve the interfacial bond strength. For instance, the bond strength of BFRP-ordinary concrete decreases by 69.0% when immersed in a 60 °C alkaline solution for 6 months, and that of BFRP-fly ash concrete decreases by 58.1% in the same immersion environment. The similar experimental phenomenon can also be obtained in seawater, which can be attributed to fly ash refining the concrete pores and inhibiting the reaction of alkaline with silica contained in the basalt fibers. Finally, the retention of bond strength is predicted based on the apparent horizontal shear strength of the BFRP.

Evaluation of Design Provisions for Horizontal Shear Strength in Composite Precast Concrete Beams with Different Interface Conditions

In a precast concrete (PC) composite beam, the horizontal interface between the PC beam and the cast-in-place (CIP) slab is located either on the compression side or on the tensile side of the cross-section. If the CIP slab is on the compression side, it becomes C-type interface, and if it is on the tensile side, it becomes T-type interface. Tensile cracks in the CIP slab may cause the horizontal shear strength of composite beams to decrease because of the reduced anchorage performance of shear reinforcements as well as the sliding on the interface. Such a tendency can be found from previous test results of specimens having T-type interface. In this study, the results of the push-off test and the beam flexure test were collected and analyzed to evaluate effects on the horizontal shear strength depending on the interface conditions, such as the interface location, surface roughness, concrete compressive strength, and clamping stress by shear connectors. The horizontal shear strength equations of ACI, PCI, AASHTO LRFD, and MC 2010 were evaluated with a database composed of 84 push-off tests and 95 beam tests from previous studies. According to the evaluation, evaluation results show that the design codes predict the horizontal shear strength conservatively for conditions other than the interface location. The horizontal shear strength deviated largely depending on the interface locations. The design codes conservatively estimate the horizontal shear strength for C-type interface, but the horizontal shear strength of T-type interface is overestimated. Based on current studies, it is recommended to use a friction coefficient of 0.7 as MC 2010 when calculating the horizontal shear strength of a composite beam with roughened T-type interface.

Study of Anisotropy Characteristics of Bogor Volcanic Soil

Anisotropy in soil results from the deposition process which describes the characteristics of the soil grains or is caused by stress or from the consequences of stresses caused during deposition and subsequent erosion. All soils behave in general anisotropy and some exhibit undrained shear strength. This study conducted 2 tests, namely the first field testing with original soil samples in the form of CPTu and dilatometer. The CPTu test's objective is to determine the vertical soil parameters, while the dilatometer is to determine the horizontal soil parameters. This study indicates that the indication of anisotropy in all shear strength tests is evident in the results of the CPTu test and the Dilatometer test. TX - UU and consolidation show that the horizontal shear strength (Suh) is greater than the vertical slope shear strength (Suv). In this case, the ratio obtained for shear strength is Suh = 1.3 Suv. And from the results of the consolidation test in the laboratory, it was found that the horizontal compression index parameter (Cc horizontal) was greater than the vertical (Cc vertical) and the horizontal coefficient of consolidation (Ch) is greater than the vertical coefficient of consolidation (Cv).

Physical-mechanical performance of bamboo scrimbers made from Bambusa rigida

Bamboo scrimbers (BCs) with excellent performances were made from Bambusa rigida (2 to 5 years old). It was found that BCs made from 3-year-old bamboo have the smallest thickness swelling (TS) and width swelling (WS). BCs prepared from 4-year-old bamboo has the maximum compressive strength (CS) and horizontal shear strength (HSS). The maximum modulus of rapture (MOR) and modulus of elastic (MOE) of BCs were observed in BCs made from bamboo with age of 5 years. Overall, the resin dosage of 11% was optimized to fabricate BCs with different maturing bamboo culms; 4-year-old bamboos were recommended to be used as the raw material for the production of BCs.

Shear Behavior of Concrete Encased Steel Truss Composite Girders

In this study, experimental tests were performed to evaluate the shear performance of encased steel truss (EST) composite girders that can resist loads at construction and composite stages. Four full-scale EST composite girders were fabricated, where the truss type (Pratt truss and Warren truss) and presence of stirrups were set as main test variables. The test results showed that in specimens applied with the Pratt truss, horizontal shear cracking occurring along the interface between concrete and steel was the dominant failure mode. Based on the crack pattern and failure plane observed from the test, the horizontal shear strengths of the Pratt truss specimens were calculated, which provided conservative results. On the other hand, in the specimens with the Warren truss inside, the strengths of the specimens were governed by the shear failure occurring in the screw rod connecting the truss elements prior to the yielding of the diagonal member. The shear strengths of the Warren truss specimens calculated based on the shear failure of the screw rod were similar to that obtained from the test.

Condition assessment of concrete and glass fiber reinforced polymer (GFRP) rebar after 18 years of service life

Concrete and glass fiber reinforced polymer (GFRP) bar samples from an 18-year old repair project executed on an existing dry-dock were obtained by coring the dry dock in two regions. Several destructive and non-destructive tests were performed on both materials. Testing performed on the concrete showed substantial variability and clear evidence of damage occurring over the years. Further, there were significant differences in the concrete obtained from two different regions of the dock. The concrete was carbonated and chloride from seawater had penetrated significantly into its depth. The GFRP bars showed relatively lower variability in terms of test results. Electron microscopy and horizontal shear strength results suggest that the GFRP surface of the bars had suffered some damage, whereas the core had remained unaltered. These findings regarding limited damage to the GFRP, taken together with recent advances in GFRP production technology, support the notion that concrete reinforced with GFRP bars is an attractive alternative to conventional steel reinforced concrete for marine infrastructure applications.

Calculation of Horizontal Shear Strength in Reinforced Concrete Composite Beams

Calculation of Horizontal Shear Strength in Reinforced Concrete Composite Beams

Experimental analysis of the shear strength of composite concrete beams without web reinforcement

Composite concrete members without web reinforcement are often used in precast construction. The contribution of the cast-in-place concrete topping slab to vertical shear strength has been traditionally disregarded. However, significant cost savings can result from designing and assessing these structures if this contribution is considered. This paper presents the experimental study of a series of 21 monolithic and composite (precast beam and cast-in-place slab) specimens without web reinforcement, and with rectangular and T-shaped cross-sections, failing in shear. The vertical shear strength was analysed by the following test variables: cross-section shape, the existence of an interface between different aged concretes, strengths of the two concretes and the differential shrinkage effect. From these experimental tests, it was concluded that the slab contributed to shear strength, the use of high-strength concrete slightly increased specimens’ shear strength and the differential shrinkage did not reduce shear strength. Specimens’ failure modes were analysed based on their shear transfer mechanisms, noticing that the arching action in the slab was considerable after critical shear crack formation. The vertical shear strength experimental results were well predicted by the codes’ formulations (Eurocode 2, Model Code 2010 and ACI 318-19) when composite beam depth was taken for the calculations instead of beam depth. Codes significantly underestimated the horizontal shear strengths of the composite specimens.

Pultruded GFRP Reinforcing Bars Using Nanomodified Vinyl Ester

Glass fiber-reinforced polymer (GFRP) reinforcing bars have relatively low shear strength, which limits their possible use in civil infrastructure applications with high shear demand, such as concrete reinforcing dowels. We suggest that the horizontal shear strength of GFRP bars can be significantly improved by nanomodification of the vinyl ester resin prior to pultrusion. The optimal content of functionalized multiwalled carbon nanotubes (MWCNTs) well dispersed into the vinyl ester resin was determined using viscosity measurements and scanning electron micrographs. Longitudinal tension and short beam shear tests were conducted to determine the horizontal shear strength of the nanomodified GFRP reinforcing bars. While the tensile strength of the GFRP reinforcing bars was improved by 20%, the horizontal shear strength of the bars was improved by 111% compared with the shear strength of neat GFRP bars pultruded using the same settings. Of special interest is the absence of the typical broom failure observed in GFRP when MWCNTs were used. Differential scanning calorimetry measurements and fiber volume fraction confirmed the quality of the new pultruded GFRP bars. Fourier-transform infrared (FTIR) measurements demonstrated the formation of carboxyl stretching in nanomodified GFRP bars, indicating the formation of a new chemical bond. The new pultrusion process using nanomodified vinyl ester enables expanding the use of GFRP reinforcing bars in civil infrastructure applications.