Two-stage design method for base isolation structures includes simplified estimation and time history analysis. Simplified estimation is used in preliminary design stage for estimating the weight and the first period of an isolated structure, the upper structure is simplified as a SDOF system. According to the expected response reduction goals and response spectrum, the first period of the isolated structure, stiffness of isolation device and number of isolation bearing can be induced. Time history analysis is employed in detail design stage, for determination and optimization of isolation device based on current standards. The author has made it realized based on the old Seismic Code. As there are some changes of provision on base isolation analysis in new code, including the value of bearing stiffness and safety factor, etc., the method mentioned above should be updated. Numerical investigation shows that for regular multi-storey frame structures, the difference of the maxium ratio of floor shear between the old and new Seismic Code increase with fortification intensity.

The Two-Stage Design Method of Isolated Structures Based on New Code for Seismic Design of Buildings

Application of the effective stress principle in unsaturated geotechnical engineering problems often requires explicit knowledge of the stress acting on the soil skeleton due to suction pore water pressure. This stress is defined herein as the suction stress. A theoretical formulation of suction stress profiles, based on the soil water characteristics curve, the soil permeability characteristic curve, and previous shear strength experimental verification, is developed. The theory provides a general quantitative way to calculate vertical suction stress profiles in various unsaturated soils under steady flow rate in the form of infiltration or evaporation.

Profiles of Steady-State Suction Stress in Unsaturated Soils

During the last decades, several macro-models have been proposed for the modelling of the infill panels' contribution to the lateral strength of frames Despite all this effort, a robust model, which takes into account the influence of the vertical load, is not yet available Furthermore, the influence of the very common case of infill walls with openings, such as windows and doors, has been neglected in all the code provisions that have been published so far In this paper, an updated macro-model, based on the equivalent pin-jointed diagonal compressive strut, is presented The proposed macro-model is able to represent the stiffening effect of the infill panel with openings by taking into account both the size of the opening and the vertical load acting on the frame Detailed and in-depth parametrical investigation, based on finite element analysis, shows that the proposed mathematical macro-model can be used as a reliable and useful tool for the determination of the equivalent compressive strut width since it accounts for a large number of parameters, which are not generally accounted for by the already available models in the literature

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A macro-modelling approach for the analysis of infilled frame structures considering the effects of openings and vertical loads

Hulu Kelang is known as one of the most landslide-prone areas in Malaysia. The area has been constantly hit by landslide hazards since 1990s. This paper provides an insight into the mechanism of rainfall-induced landslide in the Hulu Kelang area. Rainfall patterns prior to the occurrences of five selected case studies were first analyzed. The results showed that daily rainfall information is insufficient for predicting landslides in the area. Rainfalls of longer durations, i.e., 3–30 days prior to the landslides should be incorporated into the prediction model. Numerical simulations on a selected case study demonstrated that both matric suction and factor of safety decreased steadily over time until they reached the lowest values on the day of landslide occurrence. Redistribution of infiltrated rainwater in the soil mass could be a reason for the slow response of failure mechanism to rainfall. Based on 21 rainfall-induced landslides that had occurred in the area, three rainfall thresholds were developed as attempts to predict the occurrence of rainfall-induced landslide. The rainfall intensity–duration threshold developed based on the local rainfall conditions provided a reasonably good prediction to the landslide occurrence. The cumulative 3- versus 30-day antecedent precipitation index threshold chart was capable of giving the most reliable prediction with the limiting threshold line for major landslide yielded a reliability of 97.6 %.

/pdf/rainfall-induced-landslides-in-hulu-kelang-area-malaysia-2erpenlq65.pdf

Rainfall-induced landslides in Hulu Kelang area, Malaysia

An innovative system for reinforced concrete masonry walls based on the combination of vertical and horizontal trussed reinforcement is proposed. The mechanical characterization of the seismic behavior of such reinforced masonry walls is based on static cyclic tests carried out on panels with appropriate geometry. The influence of the factors influencing the in-plane cyclic behavior of concrete masonry walls, such as the horizontal reinforcement, precompression, and masonry bond pattern, is discussed. The results are analyzed in terms of failure modes and force versus displacement diagrams, from which the seismic performance is assessed based on the ductility and energy capacity dissipation. The results stressed that the increase on the precompression level leads to a stiffer and more brittle lateral behavior of the masonry walls. The presence of horizontal reinforcement ensures better control and better distribution of cracking, even if only a marginal increase of lateral strength was found in the particular testing program.

/pdf/experimental-analysis-of-reinforced-concrete-block-masonry-1lo0i6y3ul.pdf

Experimental Analysis of Reinforced Concrete Block Masonry Walls Subjected to In-Plane Cyclic Loading

Masonry is a composite non-homogeneous structural material, whose mechanical properties depend on the properties of and the interaction between the composite components - brick and mortar, their volume ratio, the properties of their bond, and any cracking in the masonry. The mechanical properties of masonry depend on the orientation of the bed joints and the stress state of the joints, and so the values of the shear modulus, as well as the stiffness of masonry structural elements can depend on various factors. An extensive testing programme in several countries addresses the problem of measurement of the stiffness properties of masonry. These testing programs have provided sufficient data to permit a review of the influence of different testing techniques (mono and bi-axial tests), the variations caused by distinct loading conditions (monotonic and cyclic), the impact of the mortar type, as well as influence of the reinforcement. This review considers the impact of the measurement devices used for determining the shear modulus and stiffness of walls on the results. The results clearly indicate a need to re-assess the values stated in almost all national codes for the shear modulus of the masonry, especially for masonry made with lime mortar, where strong anisotropic behaviour is in the stiffness properties.

Shear modulus and stiffness of brickwork masonry: An experimental perspective

This paper describes the use of an existing numerical model which is capable of generating continuous records over time of 3D soil suction profiles beneath a structure. The model uses recorded climatic data and representative soil properties. The model was used to obtain data required for the simulation of ground movements and the resulting structural response in a separate soil/structure interaction model (the results of the subsequent soil/structure interaction simulations are not reported). The factors influencing the soil moisture distribution beneath a structure were identified and careful consideration was given to quantifying the variability in these factors. The model explicitly captures the long-term moisture redistribution occurring beneath a structure as a result of introducing a ground cover. It also captures the effect of different construction dates on soil moisture conditions. If a range of construction dates are selected at random and 3D simulations over appropriate time periods are conducted, the variability in ground movements due to seasonal and long-term climatic effects and due to the choice of construction date can be quantified.

Modeling Expansive Soil Movements Beneath Structures

A computer model for the infiltration at the soil surface is described. The model has been developed for computation of seasonal suction changes in the soil profile. It simulates time dependence of the vector of sources and sinks for the finite element solution of Richard's equation. Lumped meteorological and soil parameters are used. Meteorological input to the model consists of the records for rainfall, pan evaporation, air temperature, and air humidity. As an example of an application of the model, the daily magnitudes of infiltration/evapotranspiration at the soil surface at Maryville, New South Wales, Australia, in March and April 1993 were obtained, and the resulting suction profile was calculated numerically. This example shows that the model adequately reflects major meteorological changes. The resulting suction profile correlates well with the experimental data, better than profiles resulting from the models, which assume periodic or sudden changes in surface suction.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98WR00825

An infiltration model to predict suction changes in the soil profile

The behavior of dry stack masonry (DSM) is influenced by the interaction of the infill with the frame (especially the joints between bricks), which requires further research. This study investigates the compression and shear behaviors of DSM. First, a series of compression tests were carried out on both masonry prism with mortar (MP_m) and DSM prism (MP_ds). The failure mode of each prism was determined. Different from the MP_m, the stress-strain relationship of the MP_ds was characterized by an upward concavity at the initial stage. The compression strength of the MP_ds was slightly reduced by 15%, while the elastic modulus was reduced by over 62%. In addition, 36 shear-compression tests were carried out under cyclic loads to emphasize the influence of various loads on the shear-compression behavior of DSM. The results showed that the Mohr-Coulomb friction law adequately represents the failure of dry joints at moderate stress levels, and the varying friction coefficients under different load amplitudes cannot be neglected. The experimental setup and results are valuable for further research.

/pdf/experimental-characteristics-of-dry-stack-masonry-under-46cpc6yilf.pdf

Experimental Characteristics of Dry Stack Masonry under Compression and Shear Loading

In order to improve the energy dissipation of the masonry infilled frame structure while decreasing the stiffening and strengthening effects of the infill panels, a new dry stacked panel (DSP) semi-interlocking masonry (SIM) infill panel has been developed. In this paper, the material properties of DSP and a traditional unreinforced masonry (URM) panel have been evaluated experimentally. A series of cyclic tests were performed to investigate the cyclic behaviour of the reinforcement concrete (RC) frame with different infill panels. The failure modes, damage evolution, hysteretic behaviour, stiffness degradation and energy dissipation were compared and analysed. We concluded that DSP is capable of significantly improving the seismic energy dissipation due to its hysteretic behaviour when the frame is in elastic stage without increasing the stiffness of the frame. Therefore, DSP or SIM panels can be considered as frictional dampers. Based on the experimental results, the influence of DSP was examined. Using the parallel model, the hysteretic loops of DSP subjected to different load cases were achieved. The typical full hysteretic loop for DSP could be divided into three distinct stages of behaviour: packing stage, constant friction stage and equivalent strut stage. The connection between the panel and the frame had a great effect on the transferring of different mechanical stages. The constant friction stage was verified to provide substantial energy dissipation and benefits to the ductility of the structure, which, therefore, is suggested to be prolonged in reality.

/pdf/in-plane-behaviour-of-a-reinforcement-concrete-frame-with-a-y8zkintcjv.pdf

Yuri Z. Totoev

Papers

Shear modulus and stiffness of brickwork masonry: An experimental perspective

Modeling Expansive Soil Movements Beneath Structures

An infiltration model to predict suction changes in the soil profile

Experimental Characteristics of Dry Stack Masonry under Compression and Shear Loading

In-Plane Behaviour of a Reinforcement Concrete Frame with a Dry Stack Masonry Panel.