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Civil structural health monitoring (CSHM) has become significantly more important within the last decades due to rapidly growing construction volume worldwide as well as aging infrastructure and longer service lifetimes of the structures. The utilization of distributed fiber optic sensing (DFOS) allows the assessment of strain and temperature distributions continuously along the installed sensing fiber and is widely used for testing of concrete structures to detect and quantify local deficiencies like cracks. Relations to the curvature and bending behavior are however mostly excluded. This paper presents a comprehensive study of different approaches for distributed fiber optic shape sensing of concrete structures. Different DFOS sensors and installation techniques were tested within load tests of concrete beams as well as real-scale tunnel lining segments, where the installations were interrogated using fully-distributed sensing units as well as by fiber Bragg grating interrogators. The results point out significant deviations between the capabilities of the different sensing systems, but demonstrate that DFOS can enable highly reliable shape sensing of concrete structures, if the system is appropriately designed depending on the CSHM application.

The construction technology of broken line pretensioned method, which is suitable for long-span bridges, can greatly improve the flexural strength of concrete members. To study the mechanical performance and failure mode of broken line pretensioned prestressed concrete I-beam, an I-beam with a span of 30 m was taken as the research object and on-site static load tests were carried out. Based on the ABAQUS finite element software, the numerical simulation was carried out to analyze the mechanical properties and failure behavior of the I-beam under the concentrated load, and the ultimate flexural capacity of the I-beam was studied in combination with the theoretical analysis. In addition, the optimized arrangement of prestressed tendons was analyzed. The results show that in the on-site static load tests, the strain values at the mid-span section and 1/4-span basically show a linear growth trend, and the I-beam is always in the elastic stage during the tests. The numerical simulation results are in general agreement with the test data with regard to strain, displacement, and neutral axis position. When the concentrated load reaches 1910 kN, the prestressed tendons at the bottom of the I-beam enter the yield state. The prestressed tendons play a controlling role in the ultimate bearing capacity of the I-beam. The numerical simulation result of the ultimate bending moment in the mid-span section is 3.55% larger than the theoretical analysis result, and the theoretical calculation formulas tend to be conservative. When the prestressed tendons are arranged by the four-fold point method, the I-beam has higher stiffness and bearing capacity after concrete cracking. The research results can provide a reference for the design and construction of broken line pretensioned prestressed concrete I-beam.

The behavior of reinforced concrete beams strengthened with near-surface-mounted (NSM) iron-based shape memory alloy (Fe-SMA) bars was studied. Because there were no jacking tools used to apply the prestressing force, this technique was called self-prestressing. The prestrained Fe-SMA bar was anchored inside a precut groove at the tension side of the RC beam (2000 x 305 x 150 mm [78.7 x 12.0 x 5.9 in.]). The bar was then activated through heating above 300[degrees]C (572[degrees]F), causing a prestressing force in the bar. The beam was then tested under four-point bending setup to failure. The results revealed a significant increase in the yielding and ultimate load capacities. Unlike the prestressed FRP strengthening techniques, the ductility of the beam was significantly improved due to the yielding nature of the Fe-SMA material. Keywords: anchorage; fiber-reinforced polymers; flexural strengthening; iron-based shape memory alloys; near-surface-mounted.

In practical engineering, pile foundation will be subject to the combined action of vertical and Rayleigh wave, and the existence of vertical dynamic load will cause the second-order effect that will lead to the increase of horizontal displacement. This paper presents a computational model for the effect of vertical load on the lateral response of monopole under Rayleigh wave. The pile cap is equivalent to a rigid block, and the constraint of pile head is regarded as a flexible constraint. By means of operator decomposition theory and variable separation method, the horizontal dynamic response of single-phase soil in uniform free field under Rayleigh wave propagation is obtained. The closed form solution of soil resistance under the combined action of Rayleigh wave and vertical load is obtained by means of operator decomposition theory and variable separation method. Based on Timoshenko beam theory, the dynamic differential equation of pile considering vertical load is established. A comparison with an existing solution is performed to verify the proposed solution. Through numerical examples, the effects of the vertical load, flexible constraints, dimensionless frequency and Poisson's ratio on the lateral response of monopile are assessed.

This paper investigates the seismic performance of exterior beamcolumn joints in special moment frames (SMFs) with varying axial load ratios. Cyclic testing of four additional specimens with an axial load ratio of 0.45 is compared with four companion specimens at 0.10. Each specimen was designed and constructed with Grades 60, 80, or 100 (No. 420, 550, or 690) reinforcement in accordance with ACI 318-19 provisions for special moment frame joints, except for the provisions of joint shear and confinement. While ACI 318-19 tightens confinement requirements for SMF columns and joints, especially under high axial loads, this study reveals that increasing the axial load ratio benefits joint behavior. The study also demonstrates the feasibility of using high-strength reinforcement in exterior beam-column joints of SMFs, provided that appropriate modifications are made. The findings in this study have influenced modifications from ACI 318-19 to the Building Code Requirements for Concrete Structures in Taiwan. Keywords: axial load; beam-column joint; confinement; high-strength reinforcement; joint shear; reversed cyclic loading.

This paper presents an experimental program on structural behavior of four reinforced concrete frames under column removal scenarios, simulating progressive collapse. The specimens were designed with conventional non-seismic and seismic detailing in terms of stirrup arrangement and different boundary conditions. Each specimen, consisting of a two-bay beam, a middle joint, and two side columns, was quasi-statically tested by increasing the beam deflection until the complete failure. The load-deflection relationships show the sequential mobilization of compressive arch action and catenary action in the beams. Test results indicate that beam-column connections are the most critical components in developing catenary action, and confirmed the concern in current engineering practice that the longitudinal reinforcement in beams may fail to function as effective ties due to fracture of bars under large rotations. The bar fracture was ascribed to local rotations at the connections heavily dependent on the development of fixed-end rotation.

Ultra-high performance concrete (UHPC) is a new generation concrete with extremely high tensile and compressive strength, high durability, and ductility. UHPC offers tremendous opportunities for use in new thin and slender structural concrete elements and repair of existing concrete structures and has an excellent potential to replace conventional steel reinforcement in normal concrete (NC) members. This paper investigated the potential application of a hybrid NC-UHPC beam using a thin UHPC layer on the tension face to cater to tensile stresses, eliminating the need for passive steel reinforcement. Four-point flexural load tests were performed on 24 composite beams with a thin UHPC layer overlaid with NC. The parameters considered include the thickness of the UHPC layer, depth, and span of the beam. A linear behavior categorizes the flexural behavior of the hybrid NC-UHPC beam up to the ultimate load, after which the hybrid beam shows a non-brittle failure, and softening ensues associated with cracking, increased deflection, and loss of load resisting capacity. The unfinished top surface of the UHPC layer and the overlying NC developed a full composite action without any slip. It was found that a two-day self-curing of the UHPC layer was found to be essential for the development of a strong bond between the layers. The random dispersion and orientation of steel fibers in the UHPC can lead to a decreased tensile response for larger hybrid NC-UHPC beams. The experimental results validate the potential of hybrid NC-UHPC beams as an attractive, structurally feasible, and alternative sound form of construction in terms of their high flexural strength and corrosion-free service life. The proposed unreinforced hybrid system could be used in the construction of precast beams and slabs for residential as well as industrial buildings. Further research, including full-scale load testing of the hybrid beam, is needed prior to practical applications.

Sudden failure of reinforced concrete (RC) dapped-end beams of bridges and viaducts has occurred all around the world in the last few years due to corrosion of steel bars. The danger of sudden and brittle failure is often due to pitting corrosion of steel bars, concrete crushing, and loss of bond in steel bars. In this paper, the risk of failure of reinforced dapped-end supports at the ultimate state under vertical and lateral loads is investigated, focusing on the consequences of pitting corrosion and loss of bond in steel bars. A simplified strut-and-tie model was developed to predict the load-carrying capacity of dapped-end supports. The model includes the effects of corrosion of steel bars, loss of bond, and concrete crushing due to the biaxial state of stresses. Several laboratory experimental tests regarding the flexural behavior of RC beams with dapped-end supports were collected to validate the proposed model. Keywords: corrosion; dapped-end beams; steel bars; strut-and-tie model (STM); viaduct.

Ultra-high-performance concrete (UHPC), a new cement-based material that offers high mechanical strength and good durability, has been widely applied in construction and rehabilitation projects in recent years. An optimum bending system is achieved by positioning the UHPC layer at the bottom tensile zone of the composite beam and placing the normal-strength concrete (NC) layer at the upper compression zone, which is described as the UHPC-NC composite beam. The fatigue behavior of reinforced UHPC-NC composite beams was described in this study, with an emphasis on the effects of UHPC layer thickness and fatigue load level on the fatigue life of the beam, deformation of the interface between UHPC and NC layers, as well as the bending stiffness of the beam. A total of 9 reinforced UHPC-NC composite beams were tested under cyclic loading. The test variables include UHPC layer thicknesses (zero, 200, and 360 mm), reinforcement ratios (1.184% and 1.786%), and the upper load levels (0.39~0.65). The results showed that good bonding had been achieved without delamination between UHPC and NC layers prior to the final fatigue failure of the beam, and the bending stiffness of the composite beam experienced a three-stage reduction under cyclic loading. Furthermore, an equation was proposed to predict the stiffness reduction coefficient of UHPC-NC composite beams under cyclic loading.

This study used finite element simulation and theoretical analysis to predict the crack distribution patterns that may occur during the shrinkage cracking process of rectangular timber beams. Based on the predictions, experimental specimens with six typical crack distribution patterns (I–VI) were designed. Subsequently, a four-point bending test method was employed to conduct large-sample size fracture tests on a total of 1200 small-sized Pinus sylvestris var. mongolica specimens, quantifying the effects of the crack depth, location, and distribution patterns on the specimens’ load-bearing capacity. The results indicate that when multiple cracks exist in a timber beam, their collective effect is not a simple superposition of individual cracks but a spatial distribution coupling effect. Both the depth and location of the cracks play crucial roles in their interaction. This study introduces three coefficients for evaluating the influence of cracks on timber beams, namely the load-bearing capacity coefficient (R), the decline ratio of load-bearing capacity (D), and the comprehensive crack-influence coefficient (β), which can effectively quantitatively evaluate crack damage effects. The framework established in this study, which links shrinkage crack characteristics with the load-bearing capacity of timber beams, along with the experimental data provided, can serve as a reference for the safety evaluation and scientific maintenance of historical timber components and modern timber structures with shrinkage cracks.