A Spike-shaped Anchorage For Steel Reinforced Polymer (SRP)-strengthened Concrete Structures

Steel reinforced polymer (SRP) composite has recently emerged as an effective and economical solution for strengthening of reinforced concrete (RC) structures. Premature debonding failure of unanchored SRP at low load levels generally governs the performance of RC structures strengthened with externally bonded SRP. Therefore, a novel yet simple spike-shaped anchorage system was proposed in this study to prevent the debonding failure of SRP and to improve the interfacial shear capacity. Experimental investigation through single-lap shear tests of SRP-concrete joints showed that the anchorage system changed the failure mode from composite debonding to fiber rupture. In addition, the anchorage system substantially increased the peak load and reduced the interfacial slippage of the SRP-concrete joint compared to the unanchored condition. A numerical procedure based on the finite difference method was developed to predict the full-range load response, and results matched well with the full-range experimental responses of anchored and unanchored specimens. Parametric study of the test results and numerical simulation based on finite difference method both showed that the fiber rupture failure mode could be achieved for anchors in various positions along the bonded length. The closer the anchor is to the loaded end, the less global slip was obtained when the load reached the peak value

Deep Reinforcement Learning for Approximate Policy Iteration: Convergence Analysis and a Post-Earthquake Disaster Response Case Study

Approximate Policy Iteration (API) is a Class of Reinforcement Learning (RL) Algorithms that Seek to Solve the Long-Run Discounted Reward Markov Decision Process (MDP), Via the Policy Iteration Paradigm, Without Learning the Transition Model in the Underlying Bellman Equation. Unfortunately, These Algorithms Suffer from a Defect Known as Chattering in Which the Solution (Policy) Delivered in Each Iteration of the Algorithm Oscillates between Improved and Worsened Policies, Leading to Sub-Optimal Behavior. Two Causes for This that Have Been Traced to the Crucial Policy Improvement Step Are: (I) the Inaccuracies in the Policy Improvement Function and (Ii) the Exploration/exploitation Tradeoff Integral to This Step, Which Generates Variability in Performance. Both of These Defects Are Amplified by Simulation Noise. Deep RL Belongs to a Newer Class of Algorithms in Which the Resolution of the Learning Process is Refined Via Mechanisms Such as Experience Replay And/or Deep Neural Networks for Improved Performance. in This Paper, a New Deep Learning Approach is Developed for API Which Employs a More Accurate Policy Improvement Function, Via an Enhanced Resolution Bellman Equation, Thereby Reducing Chattering and Eliminating the Need for Exploration in the Policy Improvement Step. Versions of the New Algorithm for Both the Long-Run Discounted MDP and Semi-MDP Are Presented. Convergence Properties of the New Algorithm Are Studied Mathematically, and a Post-Earthquake Disaster Response Case Study is Employed to Demonstrate Numerically the Algorithm\u27s Efficacy

Interfacial bond characteristics of fiber reinforced cementitious matrix for external strengthening of reinforced concrete members

This paper presents the results of an experimental study and discusses the applicability of a fracture mechanics based approach to understand the stress transfer mechanism of fiber reinforced cementitious matrix (FRCM) composites externally bonded to a concrete substrate. The FRCM composite was comprised of polyparaphenylene benzobisoxazole (PBO) fibers and polymer-modified cement-based mortar. This research aims to gain insight into the fundamental behavior of the bond between concrete and FRCM composites, which is critical in structural strengthening applications because complete loss of bond (debonding) generally initiates structural member failure. Single lap shear tests were conducted on specimens with composite strips bonded to concrete blocks. Parameters varied were composite bonded length and bonded width. Results were analyzed to understand the effective bond length, which can be used to establish the load-carrying capacity of the interface to design the strengthening system. Results also shed light on the interfacial behavior between fibers and matrix and highlight the role of the matrix in the stress transfer

Investigation of bond behavior of polyparaphenylene benzobisoxazole fiber-reinforced cementitious matrix composite-concrete interface

This paper presents the results of an experimental study conducted to understand the behavior and stress-transfer mechanism of fiber-reinforced cementitious matrix (FRCM) composites externally bonded to a concrete substrate for strengthening applications. The FRCM composite was comprised of a polyparaphenylene benzobisoxazole (PBO) fiber net embedded within two layers of polymer-modified cement-based mortar. Single-lap shear tests were conducted on specimens with composite strips bonded to concrete prisms. Parameters that varied were bonded length and width of composite. Additionally, the external coating layer of matrix was omitted on a limited number of specimens to examine the interfacial behavior between fibers and matrix and the role of the matrix in the stress transfer. Strain measurements along the composite bonded length were used to investigate the stress-transfer mechanism. Results suggest that the effective bond length of this composite is within the range of 250 to 330 mm (10 to 13 in.). Unlike with fiber-reinforced polymer (FRP) composites, no width effect was observed in terms of the maximum load. Finally, the stress-transfer mechanism at the matrix-fiber interfaces on either side of the fiber net was found to be unequal

Experimental investigation of FRCM-concrete interfacial debonding

This paper presents the results of an experimental study conducted to understand the stress-transfer mechanism of fiber reinforced concrete matrix (FRCM) composites externally bonded to a concrete substrate for strengthening applications. The FRCM composite was comprised of a polyparaphenylene benzobisoxazole (PBO) fiber net and polymer-modified cement-based mortar. Direct shear tests were conducted on specimens with composite strips bonded to concrete blocks. Parameters varied were composite bonded length and bonded width. Results were analyzed to understand the effective bonded length, which can be used to establish the load-carrying capacity of the interface to design the strengthening system. The normalized load carrying-capacity was plotted against the width of the composite strip to study the width effect. Finally, strain gage measurements along the bonded length were used to investigate the stress-transfer mechanism

Experimental investigation of FRCM-concrete interfacial debonding

This paper presents the results of an experimental study conducted to understand the stress-transfer mechanism of fiber reinforced concrete matrix (FRCM) composites externally bonded to a concrete substrate for strengthening applications. The FRCM composite was comprised of a polyparaphenylene benzobisoxazole (PBO) fiber net and polymer-modified cement-based mortar. Direct shear tests were conducted on specimens with composite strips bonded to concrete blocks. Parameters varied were composite bonded length and bonded width. Results were analyzed to understand the effective bonded length, which can be used to establish the load-carrying capacity of the interface to design the strengthening system. The normalized load carrying-capacity was plotted against the width of the composite strip to study the width effect. Finally, strain gage measurements along the bonded length were used to investigate the stress-transfer mechanism

Estimation of the Shear Strength of RC Members with Externally Bonded, Fully-Wrapped FRCM Composites

Externally bonded (EB) fiber reinforced cementitious matrix (FRCM) composites have been proven to be an effective solution for shear strengthening existing reinforced concrete (RC) members. Different layouts, namely U- and full-wrapping, of the EB composite can be adopted depending on the geometry and type of RC member. In the case of RC beams, the fully-wrapped layout is not always possible due to the presence of the slab. However, this layout is particularly attractive in the case of RC columns, where the composite can be applied easily and may provide significant strength increase. Although FRCM composites are attracting interest, the availability of analytical design models is still quite limited. In particular, few studies regarding the evaluation of the shear strength of FRCM fully-wrapped RC members are available in the literature. In this paper, an analytical model for the estimation of the contribution of fully-wrapped FRCM composites to the shear strength of RC members is proposed. The model is based on the truss analogy commonly adopted by various codes and guidelines for the estimation of the shear strength of RC beams and for fiber reinforced polymer (FRP) strengthened RC beams. The analytical model estimates the contribution of the FRCM to the member shear strength accounting for the bond behavior of the specific composite employed, which is an important aspect since FRCM composites have reported different bond behavior than FRP composites externally bonded to concrete substrates. The accuracy of the model provisions is assessed by comparing analytical and experimental results of RC beams fully-wrapped with a carbon FRCM composite

Numerical analysis of PBO FRCM-concrete joints

The use of fiber reinforced composites for strengthening and retrofitting existing reinforced concrete (RC) structures has been gaining popularity in the last few decades. Fiber reinforced polymer (FRP) composites have been heavily studied and proven successful for bending and shear strengthening of RC beams and slabs and for confining axially loaded RC elements. Recently, fiber reinforced cementitious matrix (FRCM) composites, which are comprised of high-strength fiber net embedded within inorganic matrices, have been proposed as an alternative to FRP composites. The bond behavior of fiber reinforced cementitious matrix (FRCM) composites applied to concrete elements is investigated in this paper by means of a three-dimensional numerical analysis. The FRCM-concrete joints studied are part of an extensive experimental campaign conducted using the single-lap direct-shear test set-up and include specimens both with and without the external layer of matrix. The input data of the numerical models are obtained applying a fracture mechanics approach that allowed for studying the shear stress – slip relationships that characterize the matrix-fiber interfaces. The load responses and strain profiles obtained from the numerical models of specimens with and without the external matrix layer are compared with the corresponding load responses and strain profiles observed in the experimental tests. A good agreement between the numerical solutions and the experimental results is obtained

Confinement of Brick Masonry Columns with SRG Jackets

This paper presents the results of an experimental program carried out to study the behavior of brick masonry columns confined by steel reinforced grout (SRG) comprised of continuous steel fiber cords embedded in a cementitious matrix. Short brick masonry columns with a square cross-section confined by SRG jackets were subjected to a monotonic concentric compressive load. Parameters investigated in this study were the area weight of steel fibers and the masonry column corner radius. Results show that the SRG jackets increased the compressive strength of the masonry columns by 26-42% relative to the unconfined masonry columns. The compressive strength of the confined columns increased slightly with increasing corner radius ratio and with increasing fiber area weight