Kohei Nagai

Bidirectional Multiple Cracking Tests on High-Performance Fiber-Reinforced Cementitious Composite Plates

This article describes how an experimental program was conducted to investigate the effects of simultaneous opening-sliding of multiple cracks on the behavior of high-performance fiber-reinforced cementitious composites (HPFRCCs). For this purpose, 12 HPFRCC plates were tested in bending and under two constitutive principal stress directions. To facilitate reorientation of the stress fields, the plates were precracked and then sawed with certain orientations. Finally, the plates were retested in bending to failure. The results showed that the change in principal stress direction had a substantial effect on macroscopic plate behavior, as marked by reductions in strength and initial stiffness. The effect of stress field reorientation on the cracking pattern was, however, minimal. Regardless of the orientation of the new principal stress direction to that of precracking, a somewhat orthogonal crack pattern always appeared. To characterize the mechanisms involved, the relationship within the constant moment span of each plate is presented and discussed.

Numerical Simulation of Failure of Anchorage with Shifted Mechanical Anchorage Bars by 3D Discrete Model

Nowadays, seismic design code in Japan is becoming more stringent. To satisfy the strict requirement, larger numbers of reinforcements must be placed, resulting in increased reinforcement congestion. To reduce the reinforcement congestion, mechanical anchorage is becoming popular in use instead of conventional hook rebar. However the behavior of mechanical anchorage placed in thin cover zone is not well understood, and the use of this is still limited. In this study, the discrete element method was used to investigate the performance of mechanical anchorage placed in thin cover depth zone, and the pull-out test in previous research was simulated. To assume that anchor plates welded to bar end are difficult to place side by side due to closely-spaced reinforcements, the position of anchor plate was taken as main parameter. The result shows that the anchorage performance changed according to the transverse bars effect and the shift of the mechanical anchorage. The simulations show good agreement with experiment data in terms of the anchorage capacity, crack pattern and failure mode.

Meso-scale Approach to Investigate the Bond Performance of Anchorage in Reinforced Concrete

To investigate the bond performance of anchorage of reinforcement in structural element, a meso-scale approach which represents the detailed description of local geometry of reinforcements, is applied. In proposed model, concrete is represented by an isotropic damage model, and material interface is defined by the interface element and cohesive zone model. Two simulation cases of simple validation tests, namely pullout test and uniaxial tension test, were carried out to study the applicability of proposed models. The analysis result indicates the proposed model has to be improved especially in description of compression behavior. However, the uniaxial tension simulation which mainly governed by tension behavior could show the typical tension stiffening behavior.

Space-averaged constitutive model for HPFRCCs with multi-directional cracking

This paper focuses on numerical modeling of high-performance fiber-reinforced cementitious composites (HPFRCCs), specifically polyvinyl alcohol engineered cement composites (PVA-ECCs) in the context of a space-averaged, fixed-crack approach. Compression, tension, and shear models are proposed. The compression and tension models include internal unloading and reloading paths. The shear model considers the shear stress transfer contributed by surface friction and fiber bridging in a phenomenological manner. The applicability of the models is verified against recent experiments on precracked PVA-ECC plates subjected to principal stress rotation, demonstrating that the proposed models replicate various responses of the plates. The degradation of initial stiffness and overall strength of plates with precracks at different angles is represented well. Lastly, this paper demonstrates the ability of the models to replicate the average strains spanning bidirectional multiple cracks occurring at the bottom surface of the precracked plates.

Prospect for Implementation of Road Infrastructure Asset Management

Infrastructure has to be adequately planned, designed, executed and maintained to keep its structural performance over respective requirements throughout its life-cycle. However, infrastructure suffering from serious deterioration in structural members and subsequent loss in performance have been often found due to various reasons. To meet these facts, it is extremely important to pursue coordination of engineering work in the stages of design, execution and maintenance. The infrastructure management including the concepts of the life-cycle management and the asset management is an organized system to support engineering-based decision making for ensuring sufficient structural performance and long life of a structure at the design, execution, maintenance, and all related work during its life-cycle. This paper deals with infrastructure management system and an example of its application for a road bridge from seriously deteriorated.

A Study on the Effect of Diagonal Cracks Opening on the Failure Behavior of RC Beam-Column Joint With Mechanical Anchorages by 3D RBSM

Local reinforcement along the anchorages can be one way to avoid anchorage failure in the beam-column joints with mechanical anchorages. However, previous experimental work showed that different macroscopic behaviors were observed with different local reinforcement arrangements. The reason for such variations was not clarified since internal stresses and internal crack conditions are not well understood. It is considered that the opening of diagonal cracks in the beam-column joint plays an important role on the failure behavior. In this study, a meso-scale discrete analysis using 3D rigid body spring model (RBSM) is conducted to investigate this consideration. Parametric studies by 3D RBSM are conducted in which stirrups along the anchorages in the joint are modeled as deformed and plain bars. Based on the simulation results, different performances are predicted with different types of stirrups. Before the occurrence of diagonal cracks, bond performance along the development length of the anchorages depends on the number of stirrup and is not affected by the type of stirrup. Once diagonal cracks occur, the opening of diagonal cracks is affected by the type of stirrup. When stirrups are modeled as plain bars, slippage occurs easily between concrete and reinforcement and diagonal cracks then open readily. Furthermore, damage occurs at the top surface of the joint, leading to a decrease in capacity.

Heterogeneous Fiber-Particle Composite Subjected to Principal Stress Rotation

Test results of 20 Engineered Cementitious Composite (ECC) plates under 4-point bending are reported. 13 plates were pre-cracked to allow rotation of the principal stress directions, in order to permit the study of shear and tensile stress transfer at multiple cracks. Coarse aggregates were investigated as a possible means to improve shear-transfer. When subjected to principal stress rotation, ECC exhibited a nearly orthogonal crack pattern, indicating little contribution from the shear transfer mechanism. A reduction in flexural capacity was observed, depending on the relative angles of principal tensile stress applied. When coarse aggregate was added to ECC, significant reductions in flexural capacity and flexural ductility were observed. In a situation when principal stress direction rotated, however, the test results show that coarse aggregate in the amount of 15% of the maximum packing density of the aggregate used was effective to control the orientation of secondary cracks in cracked ECC and to maintain a comparable level of flexural capacity irrespective of the reorientation angle of principal stress field and the angle of pre-existing cracks.

Effects of Shear Transfer on the Directions of Principal Strain Field in Cracked Concrete with Hooked Steel Fibers

This paper investigates the post-cracking behavior of steel fiber reinforced concrete (SFRC) panels from an analysis perspective based on a smeared, fixed crack approach. The analysis results show that the addition of hooked steel fibers improves the average tensile stress of the concrete and, when added beyond 1% by volume, limits the amount of crack-shear slip in the concrete effectively. The analysis reveals that experimentally observations of smaller angles of inclination of concrete principal strain than those of concrete principal stress at intermediate load levels is due to this limited crack slip. Finally, the analysis identifies that hooked steel fibers tends to be less effective than transverse reinforcement in confining shear cracks, thereby resulting in a lower shear transfer capacity.