Mark J. Masia

In-Plane Shear Behavior of Masonry Panels Strengthened with NSM CFRP Strips. I: Experimental Investigation

An experimental investigation was conducted to study the in-plane shear behavior of masonry panels strengthened with near-surface mounted (NSM) carbon fiber-reinforced polymer strips (CFRP). As part of the study four unreinforced masonry panels and seven strengthened panels were tested in diagonal tension/shear. Different reinforcement orientations were used including vertical, horizontal, and a combination of both. The effect of nonsymmetric reinforcement was also studied. The results of these tests are presented in this paper, and include the load-displacement behaviors, crack patterns, failure modes, and FRP strains. The results showed that the vertically aligned reinforcement was the most effective, with significant increases in strength and ductility observed. The dowel strength of the vertical reinforcement did not likely contribute significantly to the shear resistance of the masonry. Instead, it was likely that the vertical reinforcement acted in tension to restrain shear induced dilation and rest...

In-Plane Shear Behavior of Masonry Panels Strengthened with NSM CFRP Strips. II: Finite-Element Model

A combined experimental and numerical program was conducted to study the in-plane shear behavior of clay brick masonry walls strengthened with near surface mounting carbon-fiber-reinforced polymer (CFRP) strips. This paper is focused on the numerical program. A two-dimensional finite-element (FE) model was used to simulate the behavior of FRP-strengthened wall tests. The masonry was modeled using the micromodeling approach. The FRP was attached to the masonry mesh using the shear bond-slip relationships determined from experimental pull tests. The model was designed in a way so that FRP crossing a sliding crack (perpendicularly) would prevent crack opening, normal to the direction of sliding (dilation), and increase sliding resistance. This sliding resisting mechanism was observed in the experimental tests. The FE model reproduced the key behaviors observed in the experiments, including the load-displacement response, crack development, and FRP reinforcement contribution. The FE model did not include maso...

Numerical Investigation of Creep Effects on FRP-Strengthened RC Beams

Numerical analysis using a finite-element model was performed to simulate and investigate the long-term behavior of two RC beams with similar steel reinforcement, cast from the same batch of concrete. One beam was a plain RC beam and the other beam was strengthened using carbon fiber-reinforced polymer (FRP) strips. The deflections of both beams have been monitored for 5 years after loading. The finite-element model included both creep of concrete and viscoelasticity of the epoxy adhesive at the concrete-carbon FRP (CFRP) interface. The results of the finite-element analysis are compared to experimental observations of the two beams. The finite-element analysis was found to be able to simulate the long-term behavior of the CFRP-strengthened beam and help us understand the complex changes in the stress state that occur over time.

Creep Effects in Plain and Fiber-Reinforced Polymer-Strengthened Reinforced Concrete Beams

This study considers the potential effects of creep on reinforced concrete (RC) beams strengthened with externally applied fiber reinforced polymer (FRP) strips. The significance of creep in the epoxy adhesive and whether such creep might allow the FRP strips to unload over time is assessed. The long-term deflection behavior of two RC beams with similar dimensions and material properties was monitored. One beam was externally strengthened with fiber-reinforced polymer (FRP) strips, while the other was used as a control specimen. Both beams have been subjected to sustained loading for over 6-1/2 years. Slip movements at the ends of the FRP strips were also monitored. The experimental deflections have been compared to deflection predictions using ACI 209R-92 and CEB-FIP MC 90. The creep deformations of the FRP-strengthened beam are not as predicted from the control beam. A step-by-step in-time analysis and finite element modeling are used in the analysis, and both showed good ability to simulate long-term effects in RC beams strengthened with FRP. Results from both techniques show that creep of the adhesive layer can account for the differences observed between the predicted and actual behaviors of the beam, and that this creep should be included when assessing the long-term effects of strengthening a beam with externally applied FRP.

Experimental Evaluation of Static Cyclic In-Plane Shear Behavior of Unreinforced Masonry Walls Strengthened with NSM FRP Strips

AbstractAn experimental study was conducted to assess the effectiveness of strengthening unreinforced-masonry (URM) shear panels with near surface-mounted (NSM) fiber-reinforced polymer (FRP) strips. A total of 23 wall panels (5 URM and 18 reinforced) were subjected to vertical precompression combined with either monotonic or increasing reversing cycles of in-plane lateral displacement under fixed-fixed boundary conditions. Two wall aspect ratios (height/length) and six different reinforcement schemes were tested. The experimental program was designed to produce diagonal cracking in the URM specimens and hence investigate the effectiveness of the various reinforcement schemes in controlling this failure mode. This was achieved for the aspect ratio 1 wall panels. The study revealed that the FRP strengthening was effective in improving the ultimate load, displacement capacity, ductility, and energy dissipation compared with the URM response. For the aspect ratio 0.5 panels, base sliding failures dominated t...

Spatial Correlation of Material Properties and Structural Strength of Masonry in Horizontal Bending

AbstractSpatial variability of material properties might significantly affect the structural performance and reliability of unreinforced masonry (URM) walls. The paper develops a computational method to predict the strength for URM walls subject to one-way horizontal bending considering unit-to-unit spatial variability of the material properties of mortar joints and bricks. In this context, the term unit is being used to describe the location in the wall associated with a single brick and the adjacent mortar joints. In this way, the material properties are assumed to be uniform along the length, height, and thickness of individual bricks but may vary from brick to brick within the wall. Tensile strength, shear bond strength, and associated fracture energies of the mortar joints and tensile strength and fracture energy of the bricks are the main parameters considered herein. The authors examine how correlation and spatial variability in unit strengths (mortar joints and bricks) affect the variability of ul...

Stochastic spatial modelling of material properties and structural strength of unreinforced masonry in two-way bending

Abstract The paper describes the development of a computational method to predict the strength for unreinforced masonry walls subject to two-way out-of-plane bending considering unit-to-unit spatial variability of the material properties of mortar joints and bricks. The study involves conducting a numerical simulation of full-sized walls subject to two-way bending using stochastic analysis in the form of Monte Carlo simulations and comparing the results with experimental work. A 3-D non-linear Finite Element Analysis is used to study how the spatial variability of material properties affect non-load bearing wall failure progression. The numerical results are compared to the experimental results in terms of the wall failure progression and wall capacity. It is shown that the model which considers the spatial variability of brickwork can best capture the failure patterns and predict the cracking and ultimate loads for walls subjected to two-way bending.

An experimental and statistical analysis of the flexural bond strength of masonry walls

This paper describes an experimental program where full sized clay brick unreinforced masonry walls were constructed by masons with different levels of skills. The flexural bond strength of each joint in each wall was obtained using the bond wrench test. This provided extensive data for a statistical analysis to assess the degree of spatial correlation of that property. The analysis also included a comparison between the flexural bond strength of joints within the walls and prisms. The study recommended that flexural bond strengths between joints are statistically independent and that the commonly used prisms may not represent adequately the wall.