Numerical investigation of lateral earth pressure for unreinforced masonry walls

For the design of unreinforced masonry walls under lateral earth pressure according to DIN EN 1996‐3 [1], the active earth pressure is used, which is less than the earth pressure at rest. For the consideration of active earth pressure, a sufficient deflection of the wall is needed. It is unknown whether the deflections in reality are large enough to justify a reduction of the active earth pressure. Therefore a numerical model has been developed which considers the load‐bearing behaviour of masonry walls, with several boundary conditions being considered to estimate the effective earth pressure.     

Laboratory testing the Anaconda

Laboratory measurements of the performance of the Anaconda are presented, a wave energy converter comprising a submerged water-filled distensible tube aligned with the incident waves. Experiments were carried out at a scale of around 1:25 with a 250 mm diameter and 7 m long tube, constructed of rubber and fabric, terminating in a linear power take-off of adjustable impedance. The paper presents some basic theory that leads to predictions of distensibility and bulge wave speed in a pressurized compound rubber and fabric tube, including the effects of inelastic sectors in the circumference, longitudinal tension and the surrounding fluid. Results are shown to agree closely with measurements in still water. The theory is developed further to provide a model for the propagation of bulges and power conversion in the Anaconda. In the presence of external water waves, the theory identifies three distinct internal wave components and provides theoretical estimates of power capture. For the first time, these and other predictions of the behaviour of the Anaconda, a device unlike almost all other marine systems, are shown to be in remarkably close agreement with measurements.     

Early carbonation curing of concrete masonry units with Portland limestone cement

The effect of carbonation curing on the mechanical properties and microstructure of concrete masonry units (CMU) with Portland limestone cement (PLC) as binder was examined. Slab samples, representing the web of a CMU, were initially cured at 25 °C and 50% relative humidity for durations up to 18 h. Carbonation was then carried out for 4 h in a chamber at a pressure of 0.1 MPa. Based on Portland limestone cement content, CO₂ uptake of PLC concrete after 18 h of initial curing reached 18%. Carbonated and hydrated concretes showed comparable compressive strength at both early and late ages due to the 18-h initial curing. Carbonation reaction converted early hydration products to a crystalline microstructure and subsequent hydration transformed amorphous carbonates into more crystalline calcite. Portland limestone cement could replace Ordinary Portland Cement (OPC) in making equivalent CMUs which have shown similar carbon sequestration potential.     

Use of rice husk ash in sandcrete blocks for masonry units

Different mix proportions of sand, cement and rice husk ash (RHA) were studied for use in sandcrete blocks. Optimum water/(cement+RHA) ratios were determined at different mix proportions. Compressive strengths of various mix proportions at 7, 28 and 60 days were also determined. The optimum water/(cement+RHA) ratio increased with rice husk ash contents. Test results showed that up to 40% RHA could be added as a partial replacement for cement without any significant change in compressive strength at 60 days. Compressive strengths of various mix proportions were compared with British Statutory minimum compressive strengths of bricks for various walls and it was found that sandcrete blocks of 1∶5 mortar mixes with 40% RHA (by weight of cement) could be used in both load and non-load bearing walls.     

Hygrometry in units of a thermometric scale

Use of a single term, i.e., “dew point,” for the quantitative characteristic of gas moisture expressed in units of a thermometric scale is substantiated. Features and conditions of the correct application of this term and also calculation methods for evaluating phase equilibrium parameters in a water in the condensed state-compressed gas system are described. __________ Translated from Izmeritel'naya Tekhnika, No. 1, pp. 46–48, January, 2006.     

Mechanical behaviour of FRP-confined masonry by testing of full-scale columns

The vulnerability of masonry constructions under seismic forces, or more generally under the mechanical actions during the centuries, has been highlighted in the last years by several events that caused the loss of significant heritage buildings. Faced with this difficulty, the use of composite materials, fiber reinforced polymers (FRP) may be a solution for mitigating the vulnerability of masonry buildings. This solution has been tested in the laboratory by researchers in the last decade. In particular, studies regarding elements such as walls, arches and vaults, strengthened with FRP materials are available. A few numbers of studies are known for columns, which have been tested only as small or middle scale samples. The current state of the art does not report studies on FRP-confined masonry columns tested in real scale. The research presents the results of an experimental program performed on full-scale masonry columns strengthened with different composite systems. The same kind of study had been previously performed by the authors on medium scale masonry columns, using the same materials for both the masonry core and for the FRP system. Prismatic columns with a square cross section were subjected to compression tests according to the following test schemes: two control unconfined columns; column with continuous wrapping by using unidirectional glass FRP (GFRP) sheets; column with discontinuous wrapping by using GFRP unidirectional sheets; column with continuous GFRP wrapping and internal carbon FRP bars bonded in the transverse directions; column wrapped with continuous alkali resistant GFRP grid and steel spikes bonded together in lime based matrix. The experimental results are presented and discussed in the paper along with the comparison with the results obtained from the experimental tests on medium scale specimens. The comparison between experimental data and theoretical predictions provided by the analytical model found in the guidelines of the CNR technical document is also illustrated.     

Sorptivity: a reliable measurement for surface absorption of masonry brick units

An inherent weakness of masonry structures is low bond and bond strength. Although masonry bond is a result of many interrelated factors (e.g. surface texture, surface absorption and mortar composition, etc.), surface absorption of masonry units has a significant effect on masonry bond. Following a critical review of the current measurements of the surface absorption of masonry units, the theoretical bases of sorptivity as a measurement of surface absorption are presented. The limitations of sorptivity measurement are discussed through a review of the application of the concept of sorptivity to different porous building materials. An experimental programme to examine the surface absorption of masonry units is described. Analysis of the results showed sorptivity to be a simple and reliable measurement of surface absorption for masonry units that could be used in building standards.     

Computer-based full scale fatigue testing

Computer-based methods can help to ease the difficulties of realistic full-scale testing by unravelling some of the complexities of multi-channel service loading simulation during the stages of data acquisition, data analysis and test rig control. The potential of these methods is illustrated by a simulated gun firing test — an extreme example which requires the facilities of three widely differing computer systems to carry out full-scale endurance tests.     

Heavy metal contaminant remediation study of western Xiamen Bay sediment, China: Laboratory bench scale testing results

A surface sediment sample (<5 cm) was collected from a sewage sludge contaminated site (118°02.711′E, 24°32.585′N) within western Xiamen Bay, China, in July 2005 for a sediment decontamination study. A series of laboratory-based experiments under various conditions were performed using chemical complexation reagents (e.g., H₂C₂O₄, EDTA–2Na, etc.) and their combination in order to provide information for sediment remediation technology development. In this study, the results suggest that aeration and agitation of the sediment samples in distilled–deionized water (DDW) have either no or weak (<30%) effect on metal removal, whereas agitation, aeration and rotation of the samples in chemical complexation solutions yield much better metal removal efficiency (up to 90%). A low pH condition (e.g., pH < 3) and a low solid to liquid ratio (e.g., S:L = 1:50) could increase metal removal efficiency. The experimental results suggest that 0.20 M (NH₄)₂C₂O₄ + 0.025 M EDTA combination with solid:liquid ratio = 1:50 and 0.50 M ammonium acetate (NH₄Ac) + 0.025 M EDTA combination with solid:liquid ratio = 1:50 are the most effective methods for metal removal from the contaminated sediments. This research provides additional useful information for sediment metal remediation technology development.     

Laboratory studies of properties of the stone masonry in the Old Aswan Dam

The paper describes the results of mechanical and physical tests carried out on the masonry of the Old Aswan Dam for later assessment of its seismic stability and structural integrity. Mechanical tests were performed on 150 mm diameter cores obtained from various stages of construction of the dam. Tests indicate that the masonry in the first heightening exhibits higher strength characteristics than the masonry in the rest of the dam. Noticeably lower strength properties of the masonry in the second heightening were due to a higher water/cement ratio. The weakest link in the masonry of all three stages of construction from the point of view of its mechanical performance was the granite-mortar interfacial region. Analyses of test results show that the modulus of elasticity and the splitting tensile strength of the masonry may be expressed as a function of the compressive strength using the power regression equation and the logarithmic regression equation, respectively. The split cylinder test provides a more reliable measure of the tensile strength of the stone masonry than the direct tension test. In general, a wide scatter of test results in relation to the mean value appeared to be an inherent characteristic of this type of masonry. Variations were more pronounced in the case of the Poisson’s ratio test and in all instances when fracture at the horizontal mortar-stone interface was a primary mode of failure.     

Stress rate sensitivity of stone masonry units bound with fibre reinforced hydraulic lime mortar

It is well established that most construction materials behave differently under static and dynamic loading. However, the literature on the time-dependent response of masonry joints is scarce, particularly with regard to the bond behaviour in historical stone masonry. This paper describes the dynamic response of sandstone masonry units bound with hydraulic lime mortars (HLMs). A drop weight impact machine was used to generate stress rates up to 10⁷ kPa/s. The dynamic impact factor and stress rate sensitivity were evaluated for the flexural strength of the sandstone, mortar and for the bond strength of the unit and further, the pattern of failure was noted in the units for each mortar mix and loading rate. Based on a related study on the fracture toughness of HLM, polypropylene micro-fibres were incorporated at 0, 0.25 and 0.5% volume fraction into the mortar. Results show that the flexural bond strength was more sensitive to stress rate than the flexural strength of the mortar, at similar rates of loading. Further, the stress rate sensitivity of the bond strength decreased with an increase in the fibre content. Also, whereas the mode of failure in the masonry units under quasi-static loading was through fracture at the mortar-block interface, the failure plane transferred to within the mortar under dynamic loading, particularly in the presence of fibre reinforcement.     

An adaptive multi‐scale approach to the modelling of masonry structures

We present an adaptive multi‐scale approach for predicting the mechanical behaviour of masonry structures modelled as dynamic frictional multi‐body contact problems. In this approach, the iterative splitting of the contact problem into normal contact and frictional contact is combined with a semismooth Newton/primal‐dual active‐set procedure to calculate deformations and openings in the model structures. This algorithm is then coupled with a novel adaptive multi‐scale technique involving a macroscopic scale, which is the size of the masonry structure, and a mesoscopic scale, which is the size of the constituents (bricks, stone‐blocks), to predict appearance of dislocations and stress distribution in large‐scale masonry structures. Comparisons of the numerical results with data from experimental tests and from practical observations illustrate the predictive capability of the multi‐scale algorithm. Copyright © 2008 John Wiley & Sons, Ltd.