A Base Isolation System for Developing Countries Using Discarded Tyres Filled with Elastomeric Recycled Materials

This article studies the performance of economic base isolators using tyres filled with elastomeric recycled materials. The research was conducted to analyze base isolators to be used in developing nations, where the application of conventional elastomeric rubber bearings due to economic reasons is limited.

The tested isolators are made of kart tyres filled with different recycled elastomeric materials and aggregates. Dynamic and static tests proved acceptable vertical to horizontal stiffness ratio of the bearings and shake table tests showed an excellent enhancement of the base isolated structural response compared to the corresponding fixed base structure.     

单檐歇山式古建筑抗震性能振动台试验

为有效保护古建筑,采用振动台试验方法,研究了中国明清官式木构古建的抗震性能。以故宫某单檐歇山木构古建为对象,制作了1∶2缩尺比例模型。模型含浮放柱底、柱架、斗拱、歇山屋顶、墙体等所有构造,且施工工艺完全符合中国明清官式木构古建施工规定。通过施加白噪声激励,获得了模型的基频和阻尼比。通过施加不同强度等级的1940年El-Centro波,获得了模型典型节点的位移和加速度响应,讨论了模型的减震系数,评价了浮放柱底、榫卯节点、斗拱、屋顶、墙体等构造的抗震性能。结果表明:模型的振动形式表现为平面内的扭摆,其原因与歇山式屋顶质量分布不均密切相关。模型的震前基频为1.47Hz,阻尼比为4.6%。地震作用下,模型的位移及加速度响应曲线近似稳定、均匀。尽管屋顶构造则对地震力有一定放大作用,但浮放柱底、榫卯节点、斗拱等构造能发挥较好的耗能减震作用。对于不同构造而言,榫卯节点的减震性能最好,其减震系数可降至0.30;斗拱次之,其减震系数可降至0.53;而浮放柱底与柱顶石之间的摩擦耗能性能最弱,其减震系数最小值为0.66。墙体在地震波强度增大过程中发生倒塌,但不影响结构整体稳定性。因此,单檐歇山式木构古建具有良好的抗震性能。     

Experimental Investigation of Exterior Unreinforced Beam-Column Joints with Plain and Deformed Bars

Experimental tests on four full-scale exterior unreinforced reinforced concrete (RC) beam-column joints, representative of the existing non-conforming RC frame buildings, are carried out. The specimens have different longitudinal reinforcements (plain or deformed) and they are designed in order to be representative of two typical design practices (for gravity loads only or according to an obsolete seismic code). Different failure modes are observed, namely joint failure with or without beam yielding. The local response of the joint panel is analyzed. The different joint deformation mechanisms and their contribution to the deformability and to the energy dissipation capacity of the sub-assemblages are evaluated.     

The history of urban families in medieval England

Few medieval historians have turned their attention to the history of families in urban England. But the groundwork for such studies has been laid in previous scholarship on the merchant class, on women and work in towns, and on borough law and customs. Future studies, more specifically focused on families in towns, will draw upon a wide variety of sources including wills, property records, marriage litigation, coroner's rolls, poll taxes, borough customs, and, most importantly, borough plea rolls. These studies should allow us to explore how the special characteristics of the medieval urban environment – continual in-migration, economic opportunity, commercial and industrial diversity, extremes of wealth, high population density, and borough legal structures – affected family formation, life-cycle, demography, and domestic life in medieval towns.     

Nonlinear Static Methods vs. Experimental Shaking Table Test Results

Three different Nonlinear Static Methods (NSM's), based on pushover analysis, are applied to a 3-story, 2-bay, RC frame. They are (i) the Capacity Spectrum Method (CSM), described in ATC-40, (ii) the Displacement Coefficient Method (DCM), presented in FEMA-273 and further developed in FEMA 356, and (iii) the N2 Method, implemented in the Eurocode 8. Pushover analyses are conducted with DRAIN-3DX by using four different lateral force distributions, according to the acceleration profile assumed along the height of the structure: uniform, triangular, modal-proportional, and multimodal fully adaptive. In the numerical model, RC members are modeled as fiber elements.

The numerical predictions of each method are compared to the experimental results of the shaking table tests carried out on two similar 1:3.3-scale structural models, with and without infilled masonry panels, respectively. The comparison is made in terms of maximum story displacements, interstory drifts, and shear forces. All the NSM's are found to predict with adequate accuracy the maximum seismic response of the structure, provided that the associated parameters are properly estimated. The lateral load pattern, instead, is found to little affect the accuracy of the results for the three-story model considered, even if collapse occurs with a soft story mechanism.     

Seismic Tests and Numerical Modeling of a Rolling-ball Isolation System

For the seismic isolation of light structures, the use of laminated rubber bearings is neither economical nor, for most cases, technically suited. For the isolation of this type of structure a new system, consisting of steel balls rolling on rubber tracks, has been developed at TARRC (Tun Abdul Razak Research Centre).

This article presents the results of experimental tests carried out for the characterization of the behavior of this new device. A numerical model is also proposed that can be used to assess the seismic response of structures with this isolation system.

Comparison of the predictions of the numerical model with the experimental data shows that the model is adequate to perform the correct assessment of the seismic response of isolated structures. The results of the experimental campaign of shaking-table tests, as well as the numerical simulations, show that there is an effective reduction of the acceleration levels induced in the isolated structures.     

Shake-Table Tests of Confined-Masonry Rocking Walls with Supplementary Hysteretic Damping

A shake-table investigation is conducted on a 40% scale model frame-wall system to validate the concept of rocking walls as primary seismic systems. The rocking wall concept was implemented on confined masonry walls, but the findings can be extended to any rocking wall system. As the inherent damping of this system is low, a pair of supplemental steel hysteretic energy dissipating dampers is used at the base of the wall. It is concluded that with careful detailing, damage is not only eliminated but the structure re-centers itself following a large earthquake.     

Probabilistic Calibration and Experimental Validation of the Seismic Design Criteria for One-Story Concrete Frames

This article investigates the seismic performance of one-story reinforced concrete structures for industrial buildings. To this aim, the seismic response of two structural prototypes, a cast-in-situ monolithic frame and a precast hinged frame, is compared for four different levels of translatory stiffness and seismic capacity. For these structures an incremental nonlinear dynamic analysis is performed within a Monte Carlo probabilistic simulation. The results obtained from the probabilistic analysis prove that precast structures have the same seismic capacity of the corresponding cast-in-situ structures and confirm the overall goodness of the design criteria proposed by Eurocode 8, even if a noteworthy dependency of the actual structural behavior from the prescribed response spectrum is pointed out.

The experimental verification of these theoretical results is searched for by means of pseudodynamic tests on full-scale structures. The results of these tests confirm the overall equivalence of the seismic behavior of precast and cast-in-situ structures. Moreover, two additional prototypes have been designed to investigate the seismic behavior of precast structures with roof elements placed side by side. The results of these further tests show that an effective horizontal diaphragm action can be activated even if the roof elements are not connected among them, and confirm the expected good seismic performance of these precast systems. Finally, the results of the experimental tests are compared with those obtained from nonlinear structural analyses. The good agreement between numerical and experimental results confirms the accuracy of the theoretical model and, with it, the results of the probabilistic investigation.     

Shaking Table Model Test of a Steel-Concrete Composite High-Rise Building

Shaking table tests were conducted on a 1/20 scaled-model of a 25-story steel-concrete composite high-rise building, composed of steel frame (SF) and concrete tube (CT). The seismic behavior of the model was investigated with the increasing of table-input acceleration amplitudes. It has been found that the seismic failure of the model concentrated on the shear walls and corner columns at the lowest story of the CT as well as the joints between the SF and the CT. Even subjected to extremely strong earthquakes, due to effective composite action, the composite model was able to support its weight to prevent collapse.     

Shaking Table Testing of a Full-Scale Prefabricated Three-Story Timber-Frame Building

Shake table tests were carried out on a 7 m × 5 m three-story, timber light-frame building (7.5 m height) at the TreesLab laboratory (Eucentre) in Pavia. The aim of the research was to evaluate the seismic behavior of a typical Italian prefabricated timber building and to study the interaction between the individual structural components tested in quasi-static manner in a previous experimental study. The 1979 Montenegro Earthquake ground motion, recorded at the Ulcinj-Hotel Albatros station, was selected as the ground motion for seismic tests. The maximum peak ground acceleration was scaled to 0.07 g, 0.27 g, 0.5 g. 0.7 g, and 1 g in order to evaluate the building’s performance at different levels of seismic input. More than 100 instruments were used to monitor the behavior of the building during seismic tests measuring acceleration, displacement, and forces. The visual inspection shows that the building did not show any damage during all seismic tests. However the data analysis (dynamic identification, capacity spectrum, inter-story drift) confirm that during the 1.00 g test the structure went beyond its linear elastic limit. The results obtained from this experimental study suggest that the design hypotheses commonly adopted in practice for seismic analysis (e.g., in terms of force distributions between the walls, and also the behavior factor q) are not always consistent with the real behavior of timber frame multi-story buildings, and should be backed by more accurate knowledge of the contributions of the individual structural components.