Pre-compression Load Research Articles

In-plane and out-of-plane one-way vertical bending behavior interaction analysis of unreinforced masonry walls with newly developed load capacity interaction curve

The structural behavior of unreinforced masonry (URM) walls under in-plane (IP) or out-of-plane (OOP) loading in masonry buildings has been extensively investigated in the public literature. However, studies focusing on the URM walls subjected to concurrent IP and OOP loadings are limited. Neglecting IP and OOP interaction effects may lead to unsafe design practices. As such, this study conducts a comprehensive numerical investigation into the behavior of URM walls under combined IP and OOP loading, focusing on the influences of aspect ratio (i.e., height-to-length ratio), slenderness ratio (i.e., height-to-thickness ratio), and pre-compression load levels. To capture the possible failure modes of URM walls under various loading scenarios, the simplified micro modeling approach is employed. The analysis results indicate that the presence of OOP loading leads to a substantial reduction in IP capacities. Longer walls, characterized by smaller AR, exhibit more pronounced IP and OOP interaction effects. Additionally, highly slender walls show significant additional moments due to second-order effects under OOP loading, thereby negatively affecting the IP capacity. Low-level pre-compression loads are beneficial in diminishing capacity interaction effects, while high pre-compression loads exert a negative influence. To facilitate the consideration of IP and OOP capacity interaction effects in an efficient manner, a simplified analytical model is developed through curve fitting, in which the effects of aspect ratio, slenderness ratio, and pre-compression load are incorporated.

Numerical parametric study of dry-stack masonry walls with varied dimensional and loading configurations

In-plane behavior for masonry walls is significantly influenced by the masonry unit size and aspect ratio (height-to-length ratio). The effect of pre-compression load on the behavior of masonry walls also cannot be neglected. Several numerical and experimental research studies have been conducted to investigate behavior of these effects on masonry walls. However, said studies have not been all-inclusive, especially in regard to dry-stack masonry walls. For this study, parametric numerical simulations involving two-dimensional (2D) nonlinear models employing finite element methods (FEM) and micro-modeling approach were used to investigate the nonlinear behavior of dry-stack masonry walls with in-plane behavior under lateral load investigated by means of pushover and cyclic analyses for assorted levels of pre-compression load. Wall size, aspect ratio, and unit dimension parameters were also varied to ascertain relationship between structural behavior characteristics such as stiffness, strength, energy dissipation capacity, and failure mechanism. In general, results showed that stiffness, strength, and energy dissipation capacity decreased with increasing wall aspect ratio. Moreover, and clear relationship patterns were identified. For walls with a length of 1 m, elevating the height from 1.2 m to 2.4 m to 3.6 m leads to approximately 60% to 80% reduction in stiffness, along with approximately 50% to 60% reduction in strength. Additionally, when comparing walls with the same aspect ratio, walls with double and triple the size exhibit about 33% and 39% larger stiffnesses and about 80% and 157% larger strengths, respectively. Said results and details derived may be used in design of masonry walls, and the effects of aspect ratio, wall size, unit size, and pre-compression load under pushover and cyclic loading were considered.

Exploring the Cyclic Behaviour of URM Walls with and without Damp-Proof Course (DPC) Membranes through Discrete Element Method

Unreinforced masonry (URM) walls are common load-bearing structural elements in most existing buildings, consisting of masonry units (bricks) and mortar joints. They indicate a highly nonlinear and complex behaviour when subjected to combined compression–shear loading influenced by different factors, such as pre-compression load and boundary conditions, among many others, which makes predicting their structural response challenging. To this end, the present study offers a discontinuum-based modelling strategy based on the discrete element method (DEM) to investigate the in-plane cyclic response of URM panels under different vertical pressures with and without a damp-proof course (DPC) membrane. The adopted modelling strategy represents URM walls as a group of discrete rigid block systems interacting along their boundaries through the contact points. A novel contact constitutive model addressing the elasto-softening stress–displacement behaviour of unit–mortar interfaces and the associated stiffness degradation in tension–compression regimes is adopted within the implemented discontinuum-based modelling framework. The proposed modelling strategy is validated by comparing a recent experimental campaign where the essential data regarding geometrical features, material properties and loading histories are obtained. The results show that while the proposed computational modelling strategy can accurately capture the hysteric response of URM walls without a DPC membrane, it may underestimate the load-carrying capacity of URM walls with a DPC membrane.

Computational Modeling of Damage Progression in Unreinforced Masonry Walls via DEM

Unreinforced masonry (URM) walls are the common load-bearing elements for old masonry buildings and heritage structures. As witnessed from the past and recent earthquakes, URM walls may demonstrate various collapse mechanisms along with different crack patterns influenced by the wall aspect ratio, vertical pre-compression load, opening size and ratio, among many other factors. Typically, the mortar joints and unit-mortar interfaces are the weak planes where we expect to observe most failures, such as sliding, cracking and joint opening. However, it is not a straightforward task to simulate the structural behaviour and the failure mechanism of URM walls, including the crack localizations and propagation through the mortar joints, using the standard continuum-based computational models given the composite and highly nonlinear nature of the material. In this context, the present research offers a discontinuum-based approach to simulate the damage progression in URM walls subjected to combined shear-compression loading using the discrete element method (DEM). The masonry walls are represented via distinct elastic blocks interacting through point contacts to their surroundings. It is aimed to present the effect of the local fracture mechanism on the macro response of the masonry walls via validated DEM-based numerical models that can address all possible fracture mechanisms occurring at the unit-mortar interfaces. An innovative damage monitoring technique relying on the stress state at the point contacts is implemented and utilized to explore the associated damage progression in URM walls. The results show the great potential of the adopted modelling strategy to better understand the mechanics of URM walls and indicate the effect of strength properties of masonry constituents on the overall in-plane capacity of the load-bearing walls.

The influence of regular openings and pre-compression loading on the in-plane strength parameters of unreinforced masonry shear walls

The influence of regular openings and pre-compression loading on the in-plane strength parameters of unreinforced masonry shear walls

ITER Central Solenoid Precompression Test Mock-up – Validation phase to prepare the assembly on-site

The Central Solenoid (CS) is a key element of the ITER Magnet system, including six identical coils, called modules, assembled together to form a 4 m outer diameter, 13 m high solenoid. It is a superconducting magnet, with a peak field up to 13 T. The magnet is enclosed inside a steel structure providing vertical pre-compression and mechanical support. The room temperature pre-compression load is necessary to prevent displacement and gap between coils during the exploitation phase and therefore reduce the CS performance and create mechanical stress. The target CS pre-compression is 210 MN realized by the tightening of 45 Multi Jack Tensioners (MJTs) divided in 9 sectors. Procurement of the components and the procedures of the ITER CS is the responsibility of the USA Domestic Agency (USDA), while the ITER Organization (IO) will carry out the assembly of these components.IO signed in 2018 a collaboration agreement with CEA/IRFM to implement the pre-compression procedure proposed by the USDA using a dedicated mock-up with the main objectives:- Simulating the all modules stack rigidity with Spring plates;- Characterize the young's modulus of one CS section module;- Validating the technical procedures proposed- Estimating the time impact to accomplish the CS pre-compression process in accordance to the complete ITER Tokamak assembly.The CS mock-up Pre-compression Verification (CSPV) uses a 1/9 segment of the overall CS with a mix of ITER Tokamak and mock-up components. The target load of the mock-up is 23.3 MN to be in accordance with the overall CS pre-compression load value.This paper presents the CSPV mock-up activities, the challenges encountered and the results gained.As a conclusion, the tightening process is highlighted to estimate its applicability for the ITER CS assembly in term of technical and organisational aspects.The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.

Pull-out test and numerical simulation of beam-to-wall connection: Masonry in earthen mortar and hardwood timber

The paper investigates frictional behaviour between hardwood timber and masonry in earthen mortar, Masonry in earthen mortar and hardwood timber are typical construction materials in part of Asian countries. An experiment and numerical analysis were carried out. As the experiment, a pull-out test was performed on specimens composed of a masonry wallet and timber beam. The test was conducted under three levels of a pre-compression load. The numerical analysis was carried out to simulate the test. It focused on the discretisation of frictional behaviour in term of peak and residual friction angles and cohesion. The study helps to understand the contribution of flexible diaphragms in traditional structures.

To experimental study of performance evaluation of masonry brick bond in shear and compression in comparison

The construction of a structure is prohibitively expensive due to high material and labour expenses. Still, the production of cement, which is the most widely used binding substance in construction, results in the emission of a large amount of CO2 into the atmosphere. It has only recently been discovered that Pakistan is short of approximately 9 million residential constructions. Thus, there is a great need for cost-effective and energy-efficient masonry construction because of economic and environmental concerns. Rat-trap masonry bond creates a cavity in the wall, which serves as both thermal insulation and a cost-saving measure. Because of the inherent property of rat-trap masonry bond, a cavity is formed in the wall, which not only serves as thermal insulation for the interior but is also cost-effective It has been observed that approximately 26.11 % of the total construction cost, comprising of labor and material, can be curtailed by adopting the rat-trap bonding technique. Rat-trap bond construction is recognized as a greener and more sustainable alternative to conventional brick bonds. A comparative study of the structural behavior of the rat-trap and conventionally used English bond has been conducted. 72 prisms of rat-trap bond and English bond from three sources of bricks were tested under compression load at the ages of 28 and 56 days. The same number of prisms were tested under diagonal tension load at both ages. 18 triplet prisms from all sources of bricks were tested for shear bond strength without lateral load, whereas 5 triplet prisms from every brick source were tested with a set of lateral pre-compression loading of 29 psi, 87 psi, and 145 psi. The results show that the rat-trap bond has much higher compressive and shear strengths than the English bond.

Flexural behavior of hollow interlocking compressed stabilized earth-block masonry walls under out-of-plane loading

The present study aims to investigate the out-of-plane flexural behavior of hollow interlocking compressed stabilized earth block (ICSEB) masonry walls reinforced with bamboo and steel bars. The effect of grouting, channel block and reinforcement layout (vertical and mesh type) was assessed. A total of thirty masonry walls were fabricated using fibre reinforced blocks and categorized into five groups: two groups of ungrouted and grouted (without bamboo or steel reinforcement) masonry wall specimens and three groups of grouted masonry wall specimens reinforced with bamboo splints and steel bars. All the specimens were subjected to a constant pre-compression load while lateral load parallel to bed joints was gradually applied until failure. In addition, the experimental moment capacity of reinforced masonry walls was compared with the MSJC-11 formulations to assess the applicability. A statistical regression analysis was then performed on the test results to predict the ultimate moment and deformation capacity of all wall specimens. Test results suggest that grout alone has significantly contributed to the load carrying capacity of wall specimens but with a marginal improvement in deformability. While, channel blocks has no significant effect on load carrying capacity of reinforced grouted masonry wall specimens. Bamboo splints and steel bars as internal reinforcements are very effective in preventing the sudden failure and also enhancing the flexural resistance of masonry walls. Steel mesh showed the highest load carrying capacity, lateral deformation and energy absorption capacity. The addition of bamboo or steel reinforcement combined with grout improved the ultimate load carrying, deformation capacity and energy absorption of walls by 114.88%–260.55%, 19%–35.52% and 168.25%–489.28% respectively.The MSJC-11 code overestimated the moment capacity of reinforced masonry walls; whereas the regression models developed accurately predicted the moment capacity and lateral deformation of the masonry walls.

Joint Stiffness Influence on the First-Order Seismic Capacity of Dry-Joint Masonry Structures: Numerical DEM Investigations

Heritage masonry structures are often modelled as dry-jointed structures. On the one hand, it may correspond to the reality where the initial mortar was weak, missing, or has disappeared through time because of erosion and lixiviation. On the other hand, this modelling approach reduces complexity to the studied problem, both from an experimental and theoretical/numerical point of views, while being conservative. Still, for modelling purposes, in addition to the joint friction, numerical approaches require a specific elastic parameter, the dry-joint stiffness, which is often hard to estimate experimentally. This work numerically investigates the effect of the joint stiffness on the collapse of scaled-down tilting test experiments carried out on perforated dry-joint masonry shear walls. It is found that geometrical imperfections of bricks and the absence of vertical precompression load can lead to very low equivalent dry-joint stiffness, which strongly affects the results, both in terms of collapse and damage limit state (DLS) loads, with practical implications for the engineering practice.

Lateral force-displacement response of rat-trap bonded masonry

Rat-trap bond (RTB) masonry is one of the most economical, fast, and energy efficient construction technique for brick masonry buildings. Many developing countries including India, Nepal, Sri Lanka and Pakistan have constructed large number of buildings using this technique. However, structural stability and performance validation are as important as the economy in any construction project. Therefore, this study presents the results of in-plane quasi-static cyclic load tests on three wall specimens constructed in RTB. The pre-compression load was adjusted to simulate the load condition of a typical two storey building. The key parameters evaluated include stiffness, ductility, damping, energy dissipation, force-displacement behaviour, lateral strength, etc. The experimentally obtained results were also compared with the existing research of similar nature on conventional masonry as well as with the results predicted by various empirical equations. The comparison indicates that the lateral strength and stiffness of rat-trap masonry is significantly less than those of conventional masonry because of the reduced effective thickness, while other properties like ductility, damping and energy dissipation do not show any significant variation.

Digital image correlation for the analysis of in-plane tested unreinforced masonry walls

In the experimental assessment of the in-plane behaviour of unreinforced masonry (URM) walls containing openings, accurate measurement of the deformations occurring in the pier and spandrel substructures is important. Eight full-scale perforated URM walls were tested under in-plane cyclic loading and constant vertical pre-compression load. To measure the deformation of the walls (pier-spandrel substructures) during testing and to capture the full-field cracking of the masonry, a two dimensional (2D) Digital Image Correlation (DIC) technique was used in parallel with traditional hard-wired instrumentation (Linear Variable Differential Transformers, commonly referred to as LVDTs for short). This paper describes the detailed procedures of using DIC in large scale masonry wall testing. Firstly, the digital images at the first peak of each displacement amplitude in both push and pull directions for one specimen were analysed using the VIC-2D software to validate the DIC results against the LVDT recorded measurements. After confirming the accuracy of the DIC measurements for the specimen, the pier-spandrel movements and the cracking analyses of all the walls were performed in order to better understand the integrity of these elements during cyclic in-plane loading.

Effects of Lateral Constraints and Geometrical Characteristics on Deformation Capacity of the Persian Historic Unreinforced Masonry Shear Walls under Uncertainty Conditions

In the most structural codes, deformation capacity of the unreinforced masonry shear walls is estimated based on their structural behavior(failure mode) and aspect ratio. In this paper, deformation capacity was determined for the Persian historic brick masonry walls by considering the effects of various parameters such as lateral constraints, aspect ratio and thickness. Also, to take into account the uncertainties in material and geometry of the walls in their deformation capacity, partial factor γdu was proposed, somehow, deformation capacity of shaer wall is determined by multiplying this factor in the computed deformation. Accordingly, the in-plane behavior of 48 different specimens of masonry walls with four lateral constraint configurations (contribution of transverse walls and also top slab), four distinct aspect ratios(height to length) of 0.5, 0.75, 1.0 and 1.5, three traditional wall thicknesses of 0.20, 0.35 and 0.50 m, under pre-compression load of 0.10 MPa were computed using nonlinear pushover analyses. Then, the obtained force-deformation curves were idealized by bilinear curves (linear elastic – perfectly plastic) to make them easier for comparison objectives as well as to be more adopted in practical purposes. The latter results indicated that deformation capacity of the shear walls decreases by stiffer lateral constraints, more thickening; and decrease in height-to-length aspect ratio. In addition, it was observed that the transverse walls (vertical constraints on two sides, and at two ends of the base shear walls) were more efficient in reducing deformation capacity than the top slab (horizontal constraint). As a result, according to the numerical calculations, the ultimate drift value for the Persian historic brick masonry walls determined between 1.3% and 2.7%. Eventually, the partial factor of γdu to consider uncertainty in modulus of elasticity and thickness assessment in deformation capacity of the Persian historic masonry shear walls achieved in the range of 1.3 to 1.7.

Near-surface-mounted retrofitting of damaged/undamaged adobe walls using steel bars: Analytical evaluation of experimental results

This study examines the results of an extensive experimental program pertaining to seismic strengthening of adobe walls using near-surface-mounted (NSM) steel bars. The experiments were conducted on seven adobe wall panels (1020×800×200mm) subjected to the combined action of vertical pre-compression stresses (0.1 and 0.3 MPa) and incremental lateral loading reversals. The parameters investigated included NSM reinforcement ratio, level of vertical stress, and pre-existing damage. The load–displacement curves obtained from pushover tests were employed in the seismic evaluations using a capacity spectrum approach called the N2 method. Based on the experimental and analytical findings, the adopted retrofitting technique was found capable of effectively enhancing the in-plane seismic performance of both the undamaged and damaged adobe walls in terms of lateral strength, displacement capacity, energy dissipation, and the tolerated peak ground acceleration. It was found that the retrofitting intervention has a more beneficial contribution to the displacement capacity, rather than lateral resistance, of adobe walls under high axial pre-compression loads. Finally, analytical models originally developed for masonry walls were modified for estimating the in-plane lateral resistance of reinforced/unreinforced adobe walls.

Experimental investigation into the effect of vertical loading on in-plane cyclic behavior of adobe walls

Adobe buildings are highly susceptible to lateral loads, which is responsible for their collapse during earthquakes in the past resulting in vast damages and immense human casualties. Nonetheless, a majority of such buildings in the seismic-prone regions worldwide, including those in the Iranian plateau, are in every-day use. Thus, close examination of their behavior under lateral loading is vital for developing appropriate retrofit techniques aimed at preventing their severe damage and the associated casualties during strong ground motions. Towards this, the present experimental investigation was designed and implemented to study the in-plane lateral behavior of adobe walls under different axial pre-compression loads. The experimental program consisted of 12 adobe wall panels, all 1000 mm long and 200 mm thick but of three different heights of 800, 900, and 1000 mm. Loading was applied in the form of an incremental lateral loading regime in the presence of four vertical pre-compression stresses of 0.1, 0.3, 0.5, and 0.7 MPa. The aim was to investigate the effects of vertical loading and wall height on the in-plane lateral responses of adobe walls. The results were compared in terms of hysteretic load-displacement response, lateral resistance, displacement capacity, ductility, stiffness degradation, and energy absorption. Another aspect of the study involves a detailed examination of the failure modes and general behavior of the specimens.

Flexural behavior of rubberized concrete interlocking masonry walls under out-of-plane load

Waste and industrial by-products, such as crumb rubber and fly ash, are being utilized as raw materials for making various masonry products. Rubberized concrete interlocking brick (RIB) is a newly developed product incorporated 10% crumb rubber, as a partial replacement for sand, and 56% fly ash, as a partial replacement for cement. The study experimentally emphasized understanding the behavior of masonry walls made of the developed rubberized interlocking bricks under out-of-plane load, with and without precompression load. The compressive strength of the developed loadbearing RIB was 18.4 MPa. The results of flexural strength, moment–curvature relationship, displacement responses, joint opening, and failure modes for masonry walls made of the developed RIB under lateral load parallel to the dry bed joints are discussed. An analytical analysis to predict the cracking flexural load is presented and compared with the experimental results. The results show that by increasing the pre-compression load, flexural strength, and moment capacity of the rubberized interlocking masonry walls increased linearly. The lateral displacement was 10.82, 24.99, and 29.69 mm for masonry walls subjected to a 0, 56, and 112 kN pre-compression loads, respectively. Flexural failure along the width of masonry walls with a course opening at mid-height was the dominant failure mode. It can also be concluded that the theoretical cracking flexural load closely matches the laboratory load.

Experimental investigation of the in-plane cyclic behaviour of calcium silicate brick masonry walls

The material and structural performance of calcium silicate (CS) brick masonry has received relatively little attention in the past, although this material is often used for the construction of low-rise buildings in Central and Northern Europe. Upon the occurrence of induced seismicity in the north of the Netherlands, an extensive testing programme has been conducted since 2014 at Delft University of Technology. The paper presents the outcomes of eight quasi-static cyclic tests performed within this program on CS brick masonry walls under vertical and lateral in-plane loads. Different dimensions, boundary conditions and applied pre-compression loads were considered. Overall, the tests allowed to characterise the in-plane behaviour of CS brick masonry walls. The results confirmed the influence of the shear ratio (i.e. the ratio between the effective height and the length of the wall) on the wall response in terms of prevailing failure mode, initial stiffness, force and deformation capacity, energy dissipation. Besides, the experimental outcomes stressed the difficulty in estimating the effective stiffness and near collapse drift capacity. Additionally, an empirical equation is proposed to predict the peak lateral force. The equation, calibrated against the tests presented in this paper, was validated against an extended dataset of tests performed on CS masonry walls. The equation, which does not need any input of material parameters and is applicable irrespectively of the expected failure mode, can be used to estimate the force capacity of CS masonry walls when no or limited data on the material properties are available.

Numerical analysis and parametric study of unreinforced masonry walls with arch openings under lateral in-plane loading

This paper presents numerical modelling of the in-plane shear behaviour of unreinforced masonry (URM) walls with a semicircular arch opening. To do so, two dimensional finite element (FE) modelling of a series of experimentally tested walls was conducted using the simplified micro-modelling approach. The models successfully captured the load-displacement behaviour and, to a large extent, the failure modes of the piers and spandrels observed in the experimentally tested walls. The exception was that the FE modelling did not show pier diagonal shear cracking which was observed in some of the tested walls. The model was then used to perform parametric studies to investigate the effect of geometric variations of the walls as well as the effect of vertical pre-compression stresses on the lateral in-plane capacity of the walls. The results obtained from the FE analyses were compared to the anticipated maximum shear strength and the predicted failure modes according to the New Zealand Society for Earthquake Engineering (NZSEE, 2017). From this study, it is shown that there is a significant effect of the wall geometry and vertical pre-compression load on the failure modes and the lateral load resistance capacity of the walls. In most of the cases investigated, the NZSEE equations for maximum shear strength and failure modes agree well with the FEM results. The arch opening was remodelled to a rectangular opening and it was found that the effective pier height for an equivalent rectangular pier adjacent to a semi-circular arched opening can be taken up to the half height of the arch radius.

In-plane shear testing of unreinforced masonry walls and comparison with FEA and NZSEE predictions

The present study was conducted to investigate the global and local in-plane response of perforated URM walls under earthquake loading, based on observations of damage from previous earthquakes. To do so, full-scale cyclic in-plane testing of URM walls with an arched opening which were designed to represent walls in heritage URM structures in Australia was performed. The study investigated the behaviour of both pier and spandrel elements within the walls. Emphasis was also given to the position of walls within a multi-storey building by varying the pre-compression loads (representing gravity loads) on the walls. The tested walls were then simulated using nonlinear finite element analyses (FEA) where simplified micro-modelling (crack-shear-crush) approaches were used to analyse the wall behaviour. Finally, the shear capacities and the failure modes of the walls obtained from the experimental tests and FE analyses were compared to the proposed New Zealand Society for Earthquake Engineering (NZSEE) predictions.

In-plane Shear Testing of Unreinforced Masonry Walls and Comparison with FEA and NZSEE Predictions

The present study was conducted to investigate the global and local in-plane response of perforated URM walls under earthquake loading, based on observations of damage from previous earthquakes. To do so, full-scale cyclic in-plane testing of URM walls with an arched opening which were designed to represent walls in heritage URM structures in Australia was performed. The study investigated the behaviour of both pier and spandrel elements within the walls. Emphasis was also given to the position of walls within a multi-storey building by varying the pre-compression loads (representing gravity loads) on the walls. The tested walls were then simulated using nonlinear finite element analyses (FEA) where simplified micro-modelling (crack-shear-crush) approaches were used to analyse the wall behaviour. Finally, the shear capacities and the failure modes of the walls obtained from the experimental tests and FE analyses were compared to the proposed New Zealand Society for Earthquake Engineering (NZSEE) predictions.