Neutral Axis Research Articles

Numerical study on the behavior of eccentrically loaded square spiral-confined high-strength concrete-filled steel tube columns

Square spiral-confined concrete-filled steel tube (SCCFST) column with high-strength concrete (HSC) is a new type of composite column, which can give full play to high-strength concrete carrying capacity advantages and has good deformation capacity. A refined finite element model was developed to comprehensively investigate the compression behavior of SCCFST columns with HSC, and parametric analysis was carried out. The results demonstrated that the spiral stress developed slowly in the early loading stage but increased rapidly when the load was about 85% of the peak load. As a result, the compressive strength of concrete in the spiral-confined region was improved by about 14% when the compressive strength fc' = 111 MPa. However, the decrease in the axial load of the concrete outside the spiral-confined region offset this improvement. Thus adding the spiral had little effect (within 6%) on the load-carrying capacity of the columns while significantly improving the post-peak deformation performance. This improvement increased with the spiral confinement index increase. For a given spiral confinement index, the effect of decreasing the spiral spacing on improving the ductility of the column was the most significant. When the peak load was reached, except for the region near the neutral axis, the steel tube stress in most of the region reached the yield stress. Design expressions were derived using the plastic stress distribution method and assuming that the concrete strength in the compression zone is 0.8fc' to determine the axial load and flexural capacity of the SCCFST or CFST columns with HSC.

The Influence of a Damaged Concrete Cover on the Behavior of a Simply-Supported Beam

The concrete cover is a part of the concrete that provides the required protection for the reinforcing steel within the required element from external effects. This concrete cover can be damaged for an assortment of reasons, one of which is environmental factors. As a result, this research focused on the effect of worn concrete covering on the structural response of beams. Moreover, the possibility of repairing or replacing this concrete cover with a cement material was done by testing seven beams with the exact dimensions (2700 mm long, 250 mm deep, and 140 mm wide). The first specimen was a control specimen, while in the remaining specimens, a part of the concrete cover was removed in the midspan region with a length of 600 mm and in different formats. The part below the neutral axis (tension zone) was removed in the first two specimens. The part above the neutral axis (the compression zone) was removed in the second two specimens. The whole cover was removed within the specified distance for the other two specimens. In one out of every two of these six specimens, the removed concrete cover was replaced with cementitious material. A flexural test was performed for all specimens, and the conclusion was reached that damaging or removing the concrete cover from the tensile region (below the neutral axis) is less harmful than from the compression region since the beam is often designed as a cracked section. Also, removing the concrete cover from the compression region gives cracks a greater width than removing the concrete cover from the tension region at the same loading level. In the case of replacing the concrete cover with a cementitious one, if the replacement is in the compression zone, it will result in cracks when loading with a width greater than that of the rest of the cases. For specimens that removed their concrete covers from the tension zone, compression zone, and the whole section, the failure loads decreased by 39%, 20%, and 23%, respectively, concerning the control beam. In contrast, all these specimens were repaired with cementitious materials, with an ultimate load capacity approximately equal to the control beams. From these results, any damaged concrete cover for beams in any zone with cementitious materials having high strength and a good bond with old concrete sections can be repaired. Doi: 10.28991/CEJ-2023-09-07-09 Full Text: PDF

Investigation on structural behaviour of concrete sandwich beams with light weight composite and shear connectors

Due to rapid exhaustion of the natural resources required for building materials, there is a need in developing sustainable alternative materials. In recent years, research in the field of precast technology and lightweight structural members has been in progress. Composite Sandwich system generally consists of insulated core sandwiched between concrete wythes. The main objective of this project is to study the experimental and analytical response of Composite Sandwich Beam(CSB) under four-point flexural testing. Normally, the neutral axis of the beam has zero bending stress and shear force predominantly acts on the neutral axis. In order to reduce the usage of concrete materials and the self-weight of the beam, Expanded Polystyrene which tends to be light weight and insulated core is placed in the neutral axis portion. In order to make it much more sustainable, cement is also partially replaced by 10 % of its weight with fly ash. Truss shaped shear connectors are used which will increase the shear and ductile nature of CSB. In the analytical study, both conventional RCC and CSB are analysed and compared by using Finite Element Analysis (Ansys-APDL). Four-point flexural loading is applied on the beam specimens to assess its flexural strength experimentally. The effect of thickness of core, load–deflection curve and strain behaviour are discussed. The test results indicate that by the usage of Expanded Polystyrene as an interlayer, there is an 8.75% decrease in the total weight thereby reducing the material utilization. This leads to the development of composite material for structural beam applications without compromising its strength and it can be used in low-cost housing and green building.

Shear Strength Prediction of Reinforced Concrete Walls with Opening and Boundary Elements

Reinforced concrete (RC) walls containing openings are usually stiffened by boundary elements (or boundary flanges) in the form of columns on one or both sides. Both thickness and longitudinal reinforcement ratio of such boundary members generally exceed those of enclosed walls. Such boundary elements also contribute to an improvement in the strength of enclosed walls. As a result, the strength of RC walls with openings with boundary elements is higher than those without them. In this paper, an analytical approach based on the softened strut-and-tie model is proposed to evaluate the shear strength of RC walls with a central opening and enclosed by boundary elements. The combined behavior of the wall and boundary elements under a simultaneous bending moment and axial loading is considered in the sectional analysis to calculate neutral axis depth for evaluating strut capacity. Shear strength predictions through the proposed approach showed reasonable accuracy when verified against the test data from eleven RC walls with a single central opening. Comparisons are also made with strength estimations based on American and Japanese code provisions. Finally, a simplified equation for the evaluation of neutral axis depth is presented to enable design engineers to conduct preliminary design of RC walls with openings that are enclosed by boundary elements.

The influence of loading speed on the bending strength of beech (Fagus sp.) and birch (Betula sp.) wood

The influence of loading speed on the bending strength of beech (Fagus sp.) and birch (Betula sp.) wood The subject of this paper was to investigate the effect of loading speeds from 20 mmˑmin-1 to 200 mmˑmin-1 on the flexural strength and deformation of beech (Fagus sp.) and birch (Betula sp.) wood with moisture content close to the absolutely dry state and fibre saturation point. A GOM Aramis measuring system, operating with Digital Image Correlation (DIC) technology, was used in the study to record the displacement and deformation of the elements in real time. The results obtained for flexural strength, flexural modulus and the amount of deformation observed showed a relationship between material properties and loading rate. At higher moisture content, the bending strength and modulus of elasticity decreased with increasing deflexion. The highest bending strength and modulus of elasticity were achieved by the tested wood species at a loading rate of 200 mmˑmin-1. Beech wood, compared to birch wood, showed higher bending strength and modulus of elasticity. Images obtained by means of DIC revealed, at moisture contents close to the dry state, a symmetrical distribution of compressive and tensile stresses relative to the neutral axis of the sample cross-section. At higher moisture contents, there was a significant asymmetry between the compressive and tensile stresses and an apparent shift of the neutral axis towards the tensile surface.

Stress-strain state and load ability of compressed pipe-concrete elements

In the article are presented the results of stress-strain state and the bearing capacity of compression pipe-concrete elements studies. The studies were carried by using a fractional-rational diagram of relationship between stress and strain proposed in the Eurocode for a compressed concrete core inside a pipe and a symmetrical two-line diagram with limited area of fluidity for any values of an arbitrary flexibility of element and eccentricity of compressive force. On the carried research basis has been developed an effective numerical technique for determining the stress-strain state and the bearing capacity of compressed pipe-concrete elements. In calculation technique constructing, the task solution is reduced to system of nonlinear algebraic equations solving, relative to the deformation level in the most stressed section of the compressed concrete core section and the position of the neutral axis in this section. The efficiency of the proposed calculation method has been verified by numerous numerical experiments. It is shown that depending on the element's flexibility and the compressive force's eccentricity, at the moment of bearing capacity loss, the operation of the steel pipe can be both elastic and elasticplastic, and this is determined only by calculations using the proposed general method. Keywords: concrete; steel pipe; «load-deflection» graph; deformation; stress; deflection; stress-strain state; bearing capacity; eccentricity.

An experimental and analytical research on moment redistribution in reinforced concrete continuous beams

This paper consists of the results of experimental and analytical studies carried out to determine the moment redistribution in reinforced concrete (RC) continuous beams realistically, which are frequently used structural forms in buildings. It was determined that the parameter affecting the moment redistribution the most was the reinforcement ratio, so six RC continuous beams were produced with different reinforcement ratios. In this study, the tensile reinforcement ratio (ρ), the compressive reinforcement ratio (ρ'), and the balanced reinforcement ratio (ρb ) in the intermediate support sections are considered as the main variables, and the effects of two parameters on the moment redistribution capacities of the beams are investigated. While one of them is (ρ'/ρ), the other one is (ρ/ρb ). Considering the experimental results obtained, a simple formulation has been proposed by taking into account the neutral axis depth factor (c/d), which is the parameter frequently used in the determination of moment redistribution in the literature and in the design code provisions. Moreover, a database was created by considering the experimental results of 80 beams collected from the literature and it was aimed to determine the effectiveness of this proposed formulation compared to the equations in the literature and in the design code provisions. According to the results, it was determined that the proposed formulation gave better statistical outcomes than the others. It is thought that the design codes statistically give more negative results than the results of this study, as they generally prefer to be on the safe side deliberately. In addition to moment redistribution, the general behaviors of RC continuous beams under concentrated loads, such as load-displacement relationships, ductility, energy dissipation, and moment-curvature relationships have also been investigated in detail.

Improving the Deformability and Recovery Moment of Shape Memory Polymer Composites for Bending Actuators: Multiple Neutral Axis Skins and Deployable Core.

Shape memory polymer composite (SMPC) actuators have received significant attention for applications in space deployable structures because of their light weight and simple actuating process without any additional components. However, conventional SMPC actuators exhibit limited deformation owing to damages caused by the slight elongation of fibers and microbuckling. In this study, we designed a sandwich-structured SMPC bending actuator to increase deformability and the recovery moment with two novel features: multiple neutral axis (MNA) skins and a deployable core. The MNA skins were fabricated as layered structures of a soft layer (the polydimethylsiloxane/ethoxylated polyethylenimine layer) and hard layers (the SMPC layer) based on the MNA effect derived from the large modulus difference between the soft and hard layers. Under the bending deformation, the large shear strain in the soft layer significantly decreases the axial strain in SMPC layers and increases deformability. Applying the deployable core on the sandwich-structured SMPC bending actuator increases the recovery moment owing to the deploying force of the core. To the best of our knowledge, the sandwich-structured SMPC bending actuator composed of two MNA skins and a deployable core yielded the world's largest width-normalized recovery moment of 51.2 N·m/m with the smallest bending radius of 15 mm.

Signal-amplified stretchable PVDF kirigami sensor via neutral axis modification

Stretchable sensors with smart materials now open up diversity opportunities by suggesting ways to overcome the limitations of conventional rigid sensors. The performance of piezoelectric devices is highly dependent on piezoelectric constants. Hence, materials with low piezoelectric constants hinder users to obtain signals induced by stimuli. To rectify this problem, there have been numerous efforts to increase piezoelectricity by doping additional materials or through chemical synthesis methods. These two methods have common limitations: low cost-effectiveness and inferior accessibility by scientists from diversity of fields. In this study, we suggest methods to amplify the response of a polyvinylidene fluoride (PVDF) kirigami sensor with a structural approach: neutral axis modification with a backing layer. We introduce two sensor models with a backing layer: single side and both sides backing layer models. In the former model, the backing layer is attached to the outward area of the concave bending section for stress increment; thereby the response of the sensor can be ameliorated. For the latter model, backing layers are attached on both sides; this synchronizes stress types in the concave and convex bending sections. Consequently, it aligns current movement within the sensor. These two methods are simple and the expected results are intuitive as the voltage amplitude changes proportionally to the backing layer thickness. Also, the modified sensor exhibits stable and identical responses during and after 1000 cyclic motions of stretching and releasing with an applied strain of 80%. The maximum voltage amplitude gap between the pristine and modified sensor is marked as 8.36 V, which is a 48% amplified response from the sensor without a backing layer. This method allows users to adjust the voltage response to their demands in a simple way. This modification also has the potential to be applied as a piezoelectric energy harvesting system.

Eccentric compressive behavior of PBL-stiffened double-skin composite walls in bridge pylons

Double-skin composite walls (DSCWs) stiffened with perfobond ribs (PBLs) have gained popularity for use in large-scale structures. This investigation aims to provide valuable insights into the performance of PBL-stiffened DSCWs when subjected to eccentric compressive loads. An experimental investigation was conducted on eight PBL-stiffened DSCWs. The failure modes, local buckling behavior, load-deflection behavior, moment–curvature relationship, and strain distribution were analyzed. The results indicate that an increase in the interval of longitudinal PBLs on the compressive zone of the DSCW specimens leads to a reduction in eccentric compressive resistance due to premature local buckling. However, the transverse PBL interval and removal of transverse rebars had negligible effects on the local buckling behavior of the faceplates and did not affect the resistance of the specimens. The ductility index of DSCWs slightly increased with an increase in concrete strength and was further enhanced by the presence of headed studs. The introduction of studs on the faceplates effectively delayed the onset of local buckling and improved the resistance of the DSCWs under eccentric loads. Throughout the loading process, the longitudinal strain remained almost linear, and the neutral axes remained unchanged, indicating that the plane section assumption works for PBL-stiffened DSCWs. To develop N–M interaction curves of PBL-stiffened DSCWs under eccentric loads, the effective area method was introduced to predict the post-buckling strength of unilaterally restrained PBL-stiffened plates. The proposed curves provided accurate and relatively conservative predictions of the experimental results due to the reasonable consideration of the local buckling effect.

Flexural behavior of U-shaped steel-concrete composite beams under positive bending

The use of cold-formed U-shaped steel and concrete composite beams has increased with the advantage of permanent steel form as a load-resisting element. In this study, a new type of U-shaped steel-concrete composite beam with a bolt connection was proposed. Four-point flexural tests of full-scale specimens were performed to evaluate the flexural behavior of the composite beams under a positive bending moment. The main test parameters were the types of U-shaped steel sections and location of the neutral axis at ultimate strength. The U-shaped composite beams under positive bending behaved similarly to the composite beams with an I-shaped steel section. The strain compatibility method is recommended to evaluate the positive flexural strength of the composite beams. In addition, the effective flexural rigidity was proposed to capture the increasing trend of the flexural stiffness ratio according to the shear span-to-depth ratio.

Investigation on Flexural Fracture Behaviour of Bolted Spherical Joints with Crack Propagation in Screw Threads.

Bolted spherical joints, due to their prominent merits in installation, have been widely used in modern spatial structures. Despite significant research, there is a lack of understanding of their flexural fracture behaviour, which is important for the catastrophe prevention of the whole structure. Given the recent development to fill this knowledge gap, it is the objective of this paper to experimentally investigate the flexural bending capacity of the overall fracture section featured by a heightened neutral axis and fracture behaviour related to variable crack depth in screw threads. Accordingly, two full-scale bolted spherical joints with different bolt diameters were evaluated under three-point bending. The fracture behaviour of bolted spherical joints is first revealed with respect to typical stress distribution and fracture mode. A new theoretical flexural bending capacity expression for the fracture section with a heightened neutral axis is proposed and validated. A numerical model is then developed to estimate the stress amplification and stress intensity factors related to the crack opening (mode-I) fracture for the screw threads of these joints. The model is validated against the theoretical solutions of the thread-tooth-root model. The maximum stress of the screw thread is shown to take place at the same location as the test bolted sphere, while its magnitude can be greatly reduced with an increased thread root radius and flank angle. Finally, different design variants related to threads that have influences on the SIFs are compared, and the moderate steepness of the flank thread has been found to be efficient in reducing the joint fracture. The research findings could thus be beneficial for further improving the fracture resistance of bolted spherical joints.

Structural Behaviour of Voided Flat Slab With Various Void Ratios Under Vertical Loading

Abstract In recent modern buildings, voided slabs have been implemented because of the high reduction of their weight up to 35 %. Also, CO2 emission takes place which was developed from mass concrete. Due to percentage reduction of concrete, it leads to help the pollution free environment, eco-friendly and also more sustainable. On voided flat slabs, a minimal study has been recorded. In this current study, an approach has been made to study the effect of the position of voids in the voided flat slabs. Two groups of seven specimens each, one slab in each group was a controlled flat slab specimen with zero number of voids kept as a reference specimen, while the others were voided slabs. In each group, the number of voids were used based on the positions. The designation of the specimens is made depending on the number of voids placed and the diameter of the rebar used in the specimens. Group-A was reinforced with 8 mm diameter rebars, and Group-B was reinforced with 6 mm diameter rebars. The parameters of the study are the void positions and the rebar diameter. The specimens were subjected to a gradually concentrated load through the short column up to failure. The load carrying capacity of both voided and controlled flat slabs tested have almost same. It indicates that, the inactive concrete below the neutral axis where high density polyethylene (HDPE) recycled hollow spheres have been provided in the flat slab has shown no impact on load carrying capacity of the test specimens. However, the presence of the punching shear can be seen in the specimens where the voids are positioned near the columns and supports. Besides, ABAQUS program (A finite element based software) was used to perform the finite element analysis for profoundly illustrating the experimental findings and performing a parametric study. It is concluded that the concrete has no role at below the neutral axis of structural voided flat slab cross-section for all specimens including controlled specimens (0VS6, 0VS8). Also, it is noticed that the finite element analysis obtained results have shown more or less same as experimental results. From the present study, it is evident that behaviour of voided flat slabs are different from simply supported voided flat slabs.

Computation of physiological loading induced interstitial fluid motion in muscle standardized femur: Healthy vs. osteoporotic bone

Background and objectivesPhysiological loading-induced mechanical environments regulate bone modeling and remodeling. Thus, loading-induced normal strain is typically considered a stimulus to osteogenesis. However, several studies noticed new bone formation near the sites of minimal normal strain, e.g., the neutral axis of bending in long bones, which raises a question on how bone mass is maintained near these sites. Secondary mechanical components such as shear strain and interstitial fluid flow also stimulate bone cells and regulate bone mass. However, the osteogenic potential of these components is not well established. Accordingly, the present study estimates the distribution of physiological muscle loading-induced mechanical environments such as normal strain, shear strain, pore pressure, and interstitial fluid flow in long bones. MethodsA poroelastic finite element muscle standardized femur (MuscleSF) model is developed to compute the distribution of the mechanical environment as a function of bone porosities associated with osteoporotic and disuse bone loss. ResultsThe results indicate the presence of higher shear strain and interstitial fluid motion near the minimal strain sites, i.e., the neutral axis of bending of femoral cross-sections. This suggests that secondary stimuli may maintain the bone mass at these locations. Pore pressure and interstitial fluid motion reduce with the increased porosity associated with bone disorders, possibly resulting in diminished skeletal mechano-sensitivity to exogenous loading. ConclusionsThese outcomes present a better understanding of mechanical environment-mediated regulation of site-specific bone mass, which can be beneficial in developing prophylactic exercise to prevent bone loss in osteoporosis and muscle disuse.

Investigating the Flexural Behavior of a Two-Span High-Performance Concrete Beam Using Experimentally Derived Stress Block Parameters.

High-performance concrete (HPC) is increasingly used in construction due to its superior strength and durability. However, current stress block parameters used for designing normal-strength concrete cannot be safely applied to HPC. To address this issue, new stress block parameters have been proposed through experimental works, which are used for designing HPC members. In this study, the behavior of HPC was investigated using these stress block parameters. Two-span beams made of HPC were tested under five-point bending, and an idealized stress block curve was derived from the experimental stress-strain curve for grades 60, 80, and 100 MPa. Based on the stress block curve, equations for the ultimate moment of resistance, depth of the neutral axis, limiting moment of resistance, and maximum depth of the neutral axis were proposed. An idealized load-deformation curve was also developed, which identified four significant events: first cracking, yielding of reinforced steel, crushing of concrete with spalling of cover, and ultimate failure. The predicted values were found to be in good agreement with the experimental values, and the average location of the first crack was identified to be 0.270 L, measured from the central support on either side of the span. These findings provide important insights for the design of HPC structures, contributing to the development of more resilient and durable infrastructure.

Numerical Assessment on Continuous Reinforced Normal-Strength Concrete and High-Strength Concrete Beams

High-strength concrete (HSC) has been broadly applied to various civil structures for its advantages including high compressive strength and excellent durability and creep resistance. However, the brittleness of HSC raises concern about its use in practice. So far study on continuous reinforced HSC beams is limited. This work investigates the structural response of reinforced HSC continuous beams, and the results are compared with those of the counterparts made of normal-strength concrete (NSC). By applying a finite element method verified by experimental data, a comprehensive assessment is performed on two-span reinforced NSC and HSC (compressive strengths of 30, 60 and 90 MPa) continuous beams. A wide range of flexural reinforcement ratios are used to cover both under-reinforced and over-reinforced beams. The results show that reinforced HSC beams exhibit better flexural performance in terms of ultimate load, deformation, flexural ductility and moment redistribution, when compared to reinforced NSC beams. Formulae relating flexural ductility and moment redistribution with either neutral axis depth or tensile steel strain are suggested.

Ground kinematically aligned total knee arthroplasty: new personalized technique which enables a stable knee with deep flexion

PurposeThis study aimed to evaluate kinematically aligned total knee arthroplasty (KA-TKA) targeting the neutral ground mechanical axis (MA) (hip-to-calcaneus axis), the line from the hip centre to the bottom of the calcaneus, (ground KA-TKA) in terms of its comparison with tibia-restricted modified KA-TKA (modified KA-TKA).MethodsThis retrospective cohort study included 106 consecutive patients who underwent unilateral KA-TKA for varus osteoarthritis (OA) (60 modified KA-TKAs and 46 ground KA-TKAs). After 1:1 propensity score matching, 60 patients (30 pairs) were matched between the groups with comparable demographic data. The hip-knee-ankle (HKA) angle, coronal femoral component alignment (FCA), and coronal tibial component alignment (TCA) were compared between groups. Intraoperative soft tissue balance, including the joint component gap and varus/valgus balance, was also compared between the groups. One year postoperatively, the clinical outcomes, including the range of motion and 2011 Knee Society Score, were compared between groups.ResultsThe HKA angle and FCA/TCA were not significantly different between groups. Whereas the varus/valgus balance showed no significant differences between groups, smaller joint component gaps were found throughout the range of motion in the ground KA-TKA group than in the modified KA-TKA group. Despite no difference in clinical scores between groups, a significantly deeper postoperative flexion angle was achieved in the ground KA-TKA group than in the modified KA-TKA group (p < 0.05).ConclusionTargeting neutral ground MA in KA-TKA for patients with varus OA has the potential to provide a better flexion angle with stable intraoperative soft tissue balance.

Closed-form design solutions for parallelogram hollow structural sections under bending scenarios

Parallelogram shaped sections are compelling candidates for structural boundary members to accommodate transitions at corners and to cater for architectural aesthetics. Generally, parallelogram shaped sections possess no axis of symmetry and therefore require careful design considerations in engineering practice. However, there is limited information on this topic in the literature. This paper examined the behaviour of parallelogram shaped hollow structural sections subjected to bending moments. Closed-form solutions were derived for two types of parallelogram shaped sections (i.e., parallelogram sections and parallelogram hollow structural sections), including equations of moment inertia, general flexure equations, and equations of neutral axis. Toward practical applications, two common loading conditions were discussed, and design equations for the yield moment and plastic moments were formulated. Furthermore, the stresses at the vertices of the parallelogram were rewritten in a straightforward form as the product of a stress factor and the stress of a rectangular section. Finite element (FE) models verified by test results in the literature were developed to enable a parametric study, and the correlation among test results, FE data, and predictions by equations justified the adequacy of the proposed theoretical model and the corresponding closed-form solutions. The findings in this work show that the aspect ratio and inclination angle have a major influence on the section properties and stress distribution of parallelogram sections, whereas parallelogram hollow structural sections are further affected by an additional factor known as the shape constant. Parallelogram shaped sections may produce much greater stresses than rectangular sections under the same moments.

Investigation of thermally-induced separation in mortar-aggregate under microwave irradiation

Recycled aggregate demand is growing worldwide owing to the rapid development of public infrastructure. This paper aims to investigate the effect of multi-field coupling on the separation of mortar and aggregate based on theoretical analysis and numerical simulation, and the reliability of the models is verified by microwave heating experiment. The results indicate that the electric field intensity and temperature in mortar are greater than that in aggregate. The electric field is continuous at the interface, but there are jumps in temperature and stress. In the wave propagation plane, there are two neutral axes located respectively in mortar and aggregate. The neutral axis in mortar gradually moves towards the interface with heating time, resulting in the increase of tensile stress on mortar surface. As the tensile stress exceeds the critical strength of mortar, microcracks are appeared on the surface and then gradually propagate towards the interface. The mortar is removed from the aggregate surface as the cracks propagate to the interface. Moreover, during the heating process, dehydration of hydrous minerals and moisture migration in mortar also affect the separation of mortar and aggregate. This provides insight into the efficient separation of mortar and aggregate.

Damage Analysis of Segmental Dry Joint Full-Scale Prestressed Cap Beam Based on Distributed Optical Fiber Sensing.

Distributed fiber optic sensors (DFOS) can detect structural cracks and structural deformation with high accuracy and wide measurement range. This study monitors the segmental prestressed bent cap, assembled with a large key dry joint, based on optical fiber technology, and it allows the comparison of its damaging process with that of a monolithic cast in place counterpart. The obtained results, comprising cross-section strain distributions, longitudinal strain profiles, neutral axis location, crack pattern, and the damage process, show that the DFOS technology can be successfully used to analyze the complex working stress state of the segmental beam with shear key joints, both in the elastic range and at the ultimate load, and to successfully identify the changing characteristics of the stress state of the segmental capping beam model when elastic beam theory no longer applies. The DFOS data confirm that the shear key joint, as the weak point of the segmental cap beam, results in the high stress concentration area, and the damage rate is higher than that of the cast-in-place beam. The accurate monitoring by the DFOS allows for the realization that the damage occurs at the premature formation of a concentrated compression zone on the upper part of the shear key.