Unreinforced Clay Brick Masonry Walls Research Articles

Damage behavior and assessment of polyurea sprayed reinforced clay brick masonry walls subjected to close-in blast loads

As a means to lessen the threat of an accidental blast, the polyurea sprayed reinforcement of masonry walls has attracted extensive attention. In this research, the detailed micro numerical models which can predict the nonlinear dynamic response of unreinforced clay brick masonry walls (URWs) and polyurea reinforced clay brick masonry walls (PRWs) under close-in blast were developed. The numerical simulation results were in good agreement with the field test results. Through numerical simulation and structural resistance model, the blast resistance mechanism of polyurea was revealed, and the damage behavior of polyurea rear spraying reinforced walls (PRRWs) and polyurea double-sided spraying reinforced walls (PDRWs) under different blast scaled distance was clarified. By defining the damage parameters, i.e., internal crack rate and mass loss rate, the comprehensive effects of polyurea spraying position and blast scaled distance on the damage degree of wall were summarized. Finally, the retrieval map of damage modes for PRWs under close-in blast was established, which could provide specific guidance for the anti-blast protection design of PRWs.

Experimental and numerical study of unreinforced clay brick masonry walls subjected to vented gas explosions

A total of 16 full-scale in-situ tests were carried out to investigate the performances of unreinforced clay brick masonry walls subjected to vented gas explosions. The pressure-time histories of vented gas explosions, displacement-time histories and failure modes of wall specimens in each test were recorded and analyzed. A detailed micro model for masonry wall was developed in the finite element software LS_DYNA 971. The numerical model was validated with the test data and intensive numerical simulations were conducted to explore the influences of boundary condition, bonding pattern and thickness of masonry walls on their performances against vented gas explosions. The results show that the classical yield-line modes dominate failure patterns of masonry walls subjected to vented gas explosions and the dynamic responses of masonry walls are determined by the peak value of overpressure. It is found that boundary condition and wall thickness have great influence on the performance of masonry walls, while bonding pattern has relatively limited influence on its performance. In addition, the recorded gas explosion loads were compared with the predictions from the conventional TNT equivalency method and the methods specified in NFPA 68 and EN 14994. The results indicate both NFPA 68 and EN 14994 approaches give very conservative predictions of peak pressure from gas explosions. The TNT equivalency method also overestimates the peak pressure and predicts a load profile which is significantly different from the test data.

Limit states of modern unreinforced clay brick masonry walls subjected to in-plane loading

Recent research showed that the in-plane horizontal displacement capacity of unreinforced masonry (URM) walls depends on numerous factors that are not yet captured by current empirical drift capacity models; e.g., axial stress, shear span, geometry of the walls and the material used. In order to improve the performance-based assessment of URM wall buildings, future research should aim at developing numerical and mechanical models that link the global force-displacement response of URM walls to local deformation measures such as strains. This paper addresses the behaviour of modern clay brick masonry and makes first contributions to such an endeavour by the evaluation of experimental results: first, two sets of limit states are proposed that link local damage limit states to characteristic points of the global force-displacement response of the URM wall. The two sets define limit states for walls developing a shear or a flexural mechanism respectively. Second, local deformation measures deemed suitable for the characterisation of these limit states are evaluated from optical measurement data of quasi-static cyclic wall tests. These include strains, compression zone depth and the ratio of shear to flexural deformations.

Diagonal tension strength of vintage unreinforced clay brick masonry wall panels

An experimental program was implemented where wall panels were obtained from two existing vintage unreinforced clay brick masonry (URM) buildings and subjected to a diagonal compression loading condition in order to induce a diagonal tension failure mode. The principal aims of the experimental program were to establish the diagonal tension strength of the vintage clay brick URM walls present in the two buildings and to establish a benchmark mortar mix suitable for use when manufacturing replica clay brick test assemblages that adequately represent the strength characteristics present in vintage URM buildings. It was concluded that the use of recycled clay bricks acquired from vintage URM buildings and a mortar mix of 1:2:9 (cement:lime:sand) appropriately replicates the material strength characteristics that are present in existing vintage clay brick URM buildings located in New Zealand.

Time-Dependent Prestress Losses in Historic Clay Brick Masonry Walls Seismically Strengthened Using Unbonded Posttensioning

AbstractTime-dependent prestress losses in historic unreinforced clay brick masonry (URM) walls strengthened using unbonded posttensioning were investigated, with a particular emphasis on masonry shortening resulting from creep and shrinkage. An experimental program was undertaken that involved continuous monitoring of masonry shortening occurring in prestressed URM wallettes over a period of 180 days. The test wallettes were extracted from a real historic URM building and were subjected to varying magnitudes of prestress, representing axial stresses that would be developed at the wall base when strengthened using unbonded posttensioning. A rheological model is proposed for predicting masonry creep shortening, which can subsequently be used to predict posttensioning losses. It was established that a prestress loss of up to 16.4% for normal threaded steel bars and up to 5.4% for sheathed greased seven wire strands can be expected in posttensioned historic URM walls when the tendons are posttensioned to a s...

In-situ and laboratory based out-of-plane testing of unreinforced clay brick masonry walls strengthened using near surface mounted twisted steel bars

The out-of-plane behaviour of unreinforced masonry (URM) walls strengthened using near surface mounting of twisted steel bars (NSM-TS) was investigated by performing two series of tests, which involved in situ and laboratory based out-of-plane testing of full scale strengthened URM walls. In the first series of testing, two walls were strengthened and tested in situ inside an historic URM house located in Wellington (New Zealand), known to be originally constructed in 1884 and to have undergone several minor periodic alterations. In the second series of testing, the results of in situ testing were further confirmed by performing laboratory based reverse cyclic out-of-plane testing of two slender URM walls that were constructed using vintage solid clay bricks and a low strength hydraulic mortar, replicating typical historic URM construction. Numerous parameters pertaining to the out-of-plane behaviour of NSM-TS strengthened URM walls were investigated, including failure modes, hysteretic response curves, out-of-plane flexural strength, maximum drift, pseudo-ductility, and strain distribution in the NSM-TS bars. Finally, measured performance parameters from the strengthened walls were compared to the corresponding data from the as-built tested walls. It was inferred from the results that the observed flexural strength increase due to NSM-TS strengthening ranged from 143% to 434% when compared to the strength of as-built URM wall.

Cyclic Out-of-Plane Behavior of Slender Clay Brick Masonry Walls Seismically Strengthened Using Posttensioning

AbstractEquations for the design of a posttensioned seismic retrofit of unreinforced clay brick masonry walls are discussed, and results from an associated experimental program are reported. A total of eight full-scale multiwythe vintage solid clay brick masonry walls were subjected to uniformly distributed one-directional and reverse cyclic out-of-plane loading, of which two walls were tested as built and six walls were seismically retrofitted using unbonded posttensioning. Test wall configurations and constituent masonry materials were selected to replicate typical characteristics of historic clay brick masonry walls. The test walls were seismically retrofitted by applying varying magnitudes of posttensioning using a single tendon inserted into a cavity located at the center of each test wall. Several aspects pertaining to the seismic behavior of posttensioned masonry walls were investigated, including damage patterns, force-displacement behavior, tendon stress variation, wall secant stiffness, hysteret...