Masonry Standards Joint Committee Research Articles

In-plane shear strength and damage fragility functions for partially-grouted reinforced masonry walls with bond-beam reinforcement

This paper presents a study on the in-plane shear response of partially-grouted reinforced masonry walls with bond-beam reinforcement. A database of 95 tests on partially-grouted walls made of concrete hollow blocks was compiled from experimental studies reported in the literature to characterize the capacity and damageability of walls subjected to in-plane lateral loading. The database has been used to evaluate the accuracy of existing design shear strength equations for partially-grouted walls. It is concluded that the shear strength expressions in the Masonry Standards Joint Committee (MSJC) code and Canadian standard are unconservative for partially-grouted walls. A modified equation based on the MSJC expression is proposed which better estimates the shear strength of this type of walls. Seismic fragility functions are also derived based on the experimental database to calculate the probability of experiencing moderate and severe damage in a partially-grouted wall for a given story-drift ratio deformation or normalized shear force demand. The resulting fragility functions show that the normalized shear demand is better correlated with the level of damage than the story-drift ratio.

In-plane shear strength equation for fully grouted reinforced masonry shear walls

The flexural behavior of reinforced masonry (RM) shear walls is well defined and follows the simple flexural theory of reinforced concrete structures based on plane-section assumption. Conversely, the shear behavior of RM shear walls in the plastic hinge region is more complex due to the lack of comprehensive models that quantifies the interaction of the various mechanisms that contribute to the shear capacity. This paper aims to provide a comprehensive equation for predicting the in-plane shear strength, Vn, of RM shear walls. The proposed equation was verified against the results of 68 full-scale fully grouted RM shear walls from six sources in the literature tested under cyclic lateral excitations. The main variables considered in the experimental data were: the level of axial compressive stress, shear span to depth ratio, reinforcement ratio, anchorage end detail, and the spacing of reinforcement. Then, statistical analysis was performed to evaluate the precision of the proposed equation against ten widely-used equations, including the design equations given in the Canadian Standards Association CSA S304-14 (2014), the US Masonry Standards Joint Committee MSJC (2013), and the Standards Association of New Zealand NZS 4230:2004. The results of the statistical analysis show that the proposed equation provides a precise and sufficiently conservative prediction of the shear strength (Vn). The proposed equation conservatively accounts for the contribution of masonry and axial load (Vm+p), and horizontal reinforcement (Vs) to the shear resistance (Vn) while considering the influence of the level of ductility demand. It also considers the vertical reinforcement contribution to the in-plane shear strength.

Simplified approach to predict the flexural strength of self-centering masonry walls

This paper develops a simplified design approach to predict the flexural strength of unbonded post-tensioned masonry walls. The accuracy of different flexural expressions was investigated according to experimental and finite element modelling results. Using an analytical model and considering the stress-strain relationships for unconfined and confined masonry, force displacement curves were developed for eleven tested walls, with and without confinement plates. The developed force–displacement procedure was able to predict the lateral strength, stiffness and post-peak degradation of the behavior of the tested walls. Using a similar analytical procedure, a parametric study was performed to obtain the force-displacement response of walls with different features and to investigate the effect of different parameters including axial stress ratio, length, height and thickness of the wall, on the compression zone length. Multivariate regression analysis was performed to develop an empirical equation to estimate the compression zone length in unbonded post-tensioned walls. According to the results, the wall length and axial stress ratio were found to be the most significant factors affecting the compression zone length. Depending on the configuration of the wall, the compression zone length varied between 6.7% to 28% of the wall length. The proposed equation for compression zone length was then incorporated into the flexural analysis of post-tensioned masonry walls and validated against experimental results and finite element results. Comparing the prediction from Masonry Standards Joint Committee, MSJC (2013), and the proposed method reveals that ignoring the elongation of PT bars in strength prediction resulted in a considerable underestimation of the strength. Using the non-iterative proposed approach significantly improved the prediction.

Structural performance of reinforced interlocking blocks column

Interlocking blocks have been actively applied into current wall systems in the construction industry and limited references can be found on the axial loaded compressed column. Therefore, in this research, interlocking blocks have been innovatively assembled as columns for developing a new system that can replace the conventional concrete construction to block construction, without concrete beams and columns. These interlocking block columns are tested in the laboratory in order to investigate their structural performance under axial load. The fresh and harden properties of infills have been recorded. As the compressive strength of infill materials increased, the initial stiffness and strength showed a significant growth. An incrementing trend was also noted when increasing the reinforcement bar size. Pearson and partial correlation analysis showed infills have significant correlation with column compressive capacity. Comparison has been conducted between experimental results, Eurocode reinforced concrete and Masonry Standards Joint Committee (MSJC) design specifications. The differences were ranged from 0.65 to 1.85. Parametric study with variables of infills and reinforcement bar was carried out by adopting the Eurocode design to interlocking block columns and introducing a 0.8 reduction factor. Design recommendations have been made where the strength of infills should limit to 50MPa and reinforcement bar size should not greater than 30mm. As the dimension in assembling the column, further reduction on slenderness can be ignored.

Failure analysis and damage detection of partially grouted masonry walls by enhancing deformation measurement using DIC

This study focuses on the deformability and damaging of ungrouted and fully grouted masonry assemblages and a full-scale partially grouted (PG) reinforced masonry wall made of concrete masonry units (CMU). Traditional point-to-point method using strain gages and full-field measurement technique using digital image correlation (DIC) were implemented to investigate the damage and deformability of specimens. All the specimens were constructed in compliance with the provisions of the Masonry Standards Joint Committee (MSJC, 2013) [37] and tested under displacement controlled loading. The DIC method was used to determine non-uniform strain contours on the masonry assemblages. The method was verified by comparing the strains along the selected directions with traditional strain-gage based displacement transducer (TML model) measurements. After verifying the method, it was used to investigate the state of damage and deformability of the wall. It was concluded that full-field measurements using DIC is promising especially when the test specimens experience inelastic deformation and extensive damage. Quantitative mapping of deformation field until the wall capacity is reached was only possible by using DIC. In addition to monitoring the strains across the gage length, the DIC method provided a full-field quantitative strain map of the test specimens to wall capacity and revealed strain hot-spots associated with the maximum strain at crack locations. Characterizing the deformation mechanism and cracking of the PG reinforced masonry wall was performed by determining strain distribution and recognition of cracks corresponding to the wall capacity and strains in higher than 0.3%.

Tornado fragility and risk assessment of an archetype masonry school building

Tornadoes are a low-occurrence high-consequence hazard and not only threaten the life safety of building occupants but have recently resulted in billions of dollars in direct and indirect damages for single events. Design codes do not consider tornado loads for building and other structures (with the exception of nuclear facilities) because the occurrence rate has historically been considered too low. The advent of performance-based seismic design has revolutionized the engineering thought process and as a result building owners can consider performance objectives that enable a building to perform better in an extreme hazard than observed with current design code. In this paper, the performance of a masonry school building subjected to tornado wind loads is investigated using a fragility methodology. The tornado fragility assessment methodology is described along with proposed damage states for consideration in loss estimation. An array of masonry material types are considered based on the Masonry Standards Joint Committee (MSJC) code to enable applicability of the fragilities developed herein for a range of designs throughout the United States.

Seismic Response Evaluation of Ductile Reinforced Concrete Block Structural Walls. I: Experimental Results and Force-Based Design Parameters

The reported experimental study documents the performance of six fully grouted reinforced concrete block structural walls tested under quasistatic cyclic loading. The walls fall under the ductileshear walls and the special reinforced masonry walls seismic force resisting system (SFRS) classification of the Canadian and U.S. standards, respectively. The test matrix consisted of one rectangular, one flanged, and two slab-coupled walls, all with an overall aspect ratio of 1.4. In addition, two rectangular walls, representing the individual components of the slab-coupled wall systems, were tested to quantify the wall slab coupling effects. In addition to discussing the experimental results, the study also presents key force-based seismic design (FBSD) parameters, such as the wall lateral load capacity, plastic hinge length, wall failure modes, and displacement ductility capacities. Moreover, the effects of wall cross-sectional configuration and slab coupling on the cyclic response and deformation capabilities of the walls are discussed. In general, the yield and ultimate loads were found to be accurately predicted using the Canadian Standards Association (CSA) S304-14 and Masonry Standards Joint Committee (MSJC) formulations. The wall experimental displacement ductility values (calculated at 20% strength degradation) ranged between 5.4 and 7.6, whereas the idealized displacement ductility values at the same strength degradation level ranged between 3.4 and 5.4. The analysis results reported in the paper highlight the fact that walls designed and detailed within the same SFRS classification possess significantly different FBSD parameters. The results also indicate that slab coupling, although not recognized as a wall coupling mechanism in the current editions of the CSA and MSJC, can have significant influences on the seismic response of ductile/special reinforced masonry wall systems.

Seismic Response Evaluation of Ductile Reinforced Concrete Block Structural Walls. II: Displacement and Performance–Based Design Parameters

AbstractA typical seismically designed reinforced masonry building is composed of structural walls, constructed following the same prescriptive detailing requirements corresponding to a code classified seismic force resisting system (SFRS). However, due to architectural requirements (i.e. to allow for requirements such as openings and wall intersections), some of these walls might have the same overall aspect ratio but differ in their cross-section configurations. The companion paper presented the experimental results and force-based seismic design parameters for walls that fall under the Canadian Standards Association (CSA) ductile shear walls and the Masonry Standards Joint Committee (MSJC) special-reinforced walls SFRS classifications. The current paper utilizes the experimental results to extract key displacement-based seismic design parameters, including wall yield and ultimate curvatures, wall displacements at yield and at the post-yield stages, stiffness degradation, period elongation, and equivale...

Seismic Performance Quantification of Reinforced Masonry Structural Walls with Boundary Elements

The design of reinforced masonry (RM) structural walls subject to high inelastic curvature demands can often be hindered by prescriptive requirements in design codes regarding the ratio between compression zone depth (c) and wall length (ℓw). A possible solution to this would be the detailing of a confined boundary element at the critical wall toes to increase the curvature ductility capacity of the plastic hinge region. The Masonry Standards Joint Committee (MSJC) code currently prescribes the possible use of such boundary elements for the special reinforced masonry shear walls category. However, the MSJC provides no relevant prescriptive detailing guidance, leaving the onus on the designer to specify appropriate detailing to ensure the desired performance. The results of an experimental program designed to develop a confinement scheme based on conventional masonry construction practices are reported in this paper. Five half-scale RM walls, detailed with confined boundary elements containing a double layer of vertical reinforcement enclosed by stirrups, were tested under reversed cycles of quasi-static loading. The walls, detailed to represent typical low- to medium-rise construction, varied by their height, length, and aspect and vertical reinforcement ratios. Test results are reported in terms of force-based seismic design parameters, such as the wall strength, stiffness and ductility characteristics, as well as displacement and performance-based seismic design parameters for the next-generation of seismic codes in North America. Overall, the performance of the walls indicates that the selected boundary element detailing is a designer-friendly means of addressing the need for lower c/ℓw ratios and higher curvature levels as indicated by the MSJC.

Seismic Performance Parameter Quantification of Shear-Critical Reinforced Concrete Masonry Squat Walls

AbstractIn North America, the design of reinforced masonry (RM) shear walls as a seismic force-resisting system (SFRS) is very conservative in terms of quantifying the wall’s shear strength and ductility capacity. In the current study, eight full-scale squat RM walls were tested at McMaster University under quasi-static reversed cyclic loading to quantify their shear strength, idealized displacement ductility, drift-damage relationships, lateral stiffness degradation, and hysteretic damping. The test walls demonstrated shear-strength capacities up to 200% of those predicted by the Canadian Standards Association’s (CSA) masonry design code. In addition, the results demonstrated that the Canadian shear strength expression was, on average, 32 and 34% more conservative than the Masonry Standards Joint Committee (MSJC) and the New Zealand Standards (NZS) design codes for masonry, respectively. Moreover, the simplified modified compression field theory (SMCFT), adopted directly from the Canadian concrete design...

THE EVOLUTION OF THE DESIGN AND CONSTRUCTION OF MASONRY BUILDINGS IN THE UNITED STATES

In this paper, the process used to develop building codes in the United States of America (USA) is summarized, with emphasis on masonry. Masonry materials used in the USA are discussed. Types of masonry construction in the USA are reviewed, addressing historical as well as modern masonry. Current non-structural and structural applications of masonry in the USA are reviewed. Historical development of masonry codes in the USA is summarized, with emphasis on the current Masonry Standards Joint Committee (MSJC) Code and Specification. Future trends in that document are predicted. The paper closes with a list of challenges to the masonry industry, and a list of focused research topics intended to meet those challenges.

Verification of Masonry Building Code to Flexural Behavior of Cement-Stabilized Soil Block

AbstractMost studies involving cement-stabilized soil blocks (CSSB) concern material properties, such as the characteristics of erosion and strength and how the composition of the block affects these properties. Moreover, research has been conducted on the performance of various mortars, investigating their material properties and the tensile bond strength between CSSB units and mortar. In contrast, very little is currently known about CSSB masonry structural behavior. Because structural design codes of traditional masonry buildings were well developed over the past century, many of the same principles may be applicable to CSSB masonry buildings. This paper details the topic of flexural behavior of CSSB masonry walls and whether the Masonry Standards Joint Committee (MSJC) code can be applied to this material for improved safety of such buildings.

Force- and Displacement-Based Seismic Performance Parameters for Reinforced Masonry Structural Walls with Boundary Elements

AbstractThere is a need to evaluate existing, and introduce new, masonry construction techniques within a performance-based seismic design context to advance their adoption in the next generation of seismic design codes in North America. In this regard, a reinforced masonry (RM) structural wall system that incorporates confining boundary elements in the plastic hinge region presently lacks specific design requirements in the Masonry Standards Joint Committee and Canadian Standards Association S304.1 design codes. In addition, RM structural wall systems are omitted completely from the plan to develop a new performance-based seismic design methodology laid out by FEMA 445. This paper presents experimental results of four specially detailed RM structural walls subjected to fully reversed cycles of displacement-controlled loading as tested by the authors. In addition, the resulting analysis also includes one wall from a previous study for comparison purposes. All walls were detailed with lateral reinforcing t...

Static Cyclic Response of Partially Grouted Masonry Shear Walls

This research investigated the shear behavior of five full-scale partially grouted masonry shear walls (PG-MWs). The walls were built using concrete masonry units, with horizontal reinforcement ratios ranging from 0.085 to 0.169%. The specimens had horizontal spacing between vertical grouted cells ranging from 610 (24 in.) to 1,219 mm (48 in.). All the specimens were tested under constant gravity load and incrementally increasing in-plane loading cycles. This research showed that there appears to be a maximum horizontal reinforcement ratio after which no additional shear capacity is achieved. As indicated by the experimental results, the maximum value appears to be approximately 0.1% for specimens with horizontal spacing between vertical grouted cells of 1,219 mm (48 in.). Increasing the horizontal reinforcement beyond this level did not increase the shear strength of the test specimens. In addition, the current provisions of the Masonry Standards Joint Committee (MSJC), the New Zealand code for masonry structures, Fattal’s model, and the strut and tie model were used to predict the shear strengths of the test specimens. The current MSJC shear equations overestimated the strength of PG-MWs with horizontal spacing between the vertical grouted cells of 1,219 mm (48 in.). A significant source of this error is from overestimating the contribution of the horizontal reinforcement. In addition, the current MSJC equations overestimated the masonry contribution to the shear strength of PG-MWs. For partially grouted walls with horizontal spacing between vertical grouted cells of 813 mm (32 in.) or less, and a horizontal reinforcement ratio of 0.085%, the MSJC shear equations are adequate. Shear equations by other codes and researchers were unconservative, as well. The strut and tie models were able to predict the shear strength of the test specimens within ±16%.

Shear Behavior of Corrugated Tie Connections in Anchored Brick Veneer–Wood Frame Wall Systems

An experimental study was carried out to investigate the shear behavior of corrugated metal ties anchoring brick veneer walls to light wood frame backing. Connection subassemblies were tested under monotonic and cyclic shear, simulating in-plane loading of veneer wall systems, and statistical analyses were conducted to identify and quantify the parameters influencing their behavior. Force-displacement curves obtained under monotonic loading can be considered an upper bound for the hysteresis loop envelopes. Fastener slippage during cyclic loading enabled by the localized damage of the surrounding wood fibers diminished the energy dissipation capacity of the connection and caused pronounced pinching in the hystereses. When corrugated ties with minimum thickness permitted by the Masonry Standards Joint Committee (MSJC) Code were considered under in-plane loading, tie design and bend eccentricity were found to be the most important factors, while tie location in the bed joint, fastener type, and fastener qua...

Characteristics of Rectangular, Flanged, and End-Confined Reinforced Concrete Masonry Shear Walls for Seismic Design

This paper contains detailed analyses of an experimental study conducted to evaluate the ductility, stiffness degradation and energy dissipation characteristics of rectangular, flanged, and end-confined reinforced masonry (RM) shear walls failing in flexure. The test program consisted of seven two- and three-story RM shear walls, with aspect ratios of 1.5 and 2.2, tested under reversed cyclic lateral displacements simulating seismic loading effects. Documentation of the compressive strains at the wall toes, wall base curvatures, and ductility levels attained are presented. The paper focuses on determining the extent of plasticity over the wall height, evaluating the contribution of flexure and shear deformations to the overall wall lateral displacements, identifying the trend of stiffness degradation, and quantifying the amount of energy dissipation. The rectangular walls displacement predictions at ultimate loads using Canadian Standards Association (CSA) S304.1 were in better agreement with the experimental results compared to the Masonry Standards Joint Committee (MSJC) code predictions. However, both the MSJC code and the CSA S304.1 significantly overestimated the test results for the flanged and end-confined walls. Analysis of the measured displacements showed that the contribution of shear displacement to the overall wall displacement was, on average, 21 and 25% of the total displacement for the walls with aspect ratio of 2.2 and 1.5, respectively. The relationship between the energy dissipation and the ratio of the postyield to the yield displacements was found to be almost linear for the test walls. In addition, the wall stiffnesses degraded rapidly to about 60% of their gross stiffness at very low drift levels (0.1% drift). Measured compressive strain at the wall toes were almost double those specified in both North American codes. Extent of plasticity over the wall height was about 75% of the wall length. The data presented in this paper is expected to facilitate better understanding of RM wall behavior under in-plane load to researchers, practicing engineers, and code developers. This study aimed at presenting the flanged and end-confined categories as cost-effective alternatives to enhance the seismic performance of midrise RM construction in North America.

In-Plane Behavior of Partially Grouted Reinforced Concrete Masonry Shear Walls

The objectives of this research were to experimentally establish the in-plane behavior of partially grouted (PG) reinforced concrete masonry shear walls and to assess the appropriateness of current seismic design provisions for such walls. To accomplish these, four PG special reinforced masonry shear walls (SRMSWs) were constructed based on the provisions of the Masonry Standards Joint Committee (MSJC) code and subjected to in-plane reversed cyclic displacements. The experimental test variables included mortar formulation, level of axial stress, and boundary conditions. The results of this study indicate that PG masonry shear walls respond similar to in-filled frames and provide little coupling between vertical reinforcing steels. Using these results along with those from past research, it is shown that the shear strength expression for reinforced masonry shear walls provided by MSJC (along with others) appears unconservative for PG masonry shear walls. In terms of displacement ductility, the results indicate that the response of PG SRMSW is consistent with the R factors provided by the 2006 International Building Code due to the required capacity design and increased shear demand provisions of the MSJC.

Tendon Stress in Unbonded Posttensioned Masonry Walls at Nominal In-Plane Strength

Accurate estimation of stress in unbonded tendons at the nominal strength limit state is essential for calculating the in-plane flexural strength of posttensioned masonry walls. These walls gain their lateral strength and desirable seismic properties through the utilization of vertical unbonded posttensioning. Unlike walls with bonded tendons where the tendon stress can be found through strain compatibility with the surrounding masonry, the stress in unbonded tendons results from wall deformation between the two tendon anchorages. International masonry codes, including ASCE 5-05 (Masonry Standards Joint Committee), provide varying equations for calculating tendon stress at the nominal strength limit state but in no case have these equations been verified for in-plane loading. A finite-element model validated against large-scale in-plane structural testing of posttensioned concrete masonry walls is used to demonstrate the accuracy of existing code equations. A revised equation is then shown to provide a more accurate prediction of tendon stress for walls loaded in-plane and is recommended for inclusion in future masonry code revisions.

Behavior of masonry in the Northridge (US) and Tecomán–Colima (Mexico) earthquakes: Lessons learned, and changes in US design provisions

The Northridge earthquake (near Los Angeles, CA, USA, January 17, 1994) and the Tecomán–Colima earthquake (near Manzanillo, México, January 21, 2003) have increased our knowledge of the behavior of masonry buildings in significant earthquakes, and also have led to changes or proposals for changes in US masonry design provisions. In this paper, the masonry code-development process in the US is briefly reviewed, with emphasis on the fundamental role of the Masonry Standards Joint Committee (MSJC). The Northridge and Tecomán–Colima earthquakes are discussed, with emphasis on the behavior of modern engineered masonry. Lessons learned from those earthquakes with regard to masonry are summarized, and the related evolution of MSJC design provisions for the US is discussed.

Restraint Effectiveness in Unbonded Tendons for Prestressed Masonry

Currently, the Masonry Standards Joint Committee does not provide any guidance on the design of intermittent restraint systems. Posttensioned masonry is most cost-effective when the amount of restraint necessary to provide adequate performance is minimized. This paper presents an analytical approach to determining the force transferred between the restraint and the tendon. In addition, experimental results of component testing on restraints are presented. Specimens tested include restraints formed by filling cells with mortar and grout as well as the use of a bar positioner. Analytical methods to predict the restraint capacity are also presented and compared with the results of the component testing. Finally, design provisions are suggested along with a design example problem.