PROCEDURE AND SPECTRA FOR ANALYSIS OF RC STRUCTURES SUBJECTED TO STRONG VERTICAL EARTHQUAKE LOADS

Abstract

In view of the compendium of field evidence and supporting analysis work indicating the possible damaging effects of vertical earthquake ground motion, this paper addresses the problem of code-type vertical force calculation. In light of recent engineering seismology studies of the relationship between vertical and horizontal peak ground acceleration, the inadequacy of the 2/3-rule depicted by codes is highlighted. A simple piece-wise linear relationship is proposed and shown to represent existing strong-motion measurements adequately. Bilinear and inelastic spectra are derived and studied. It is demonstrated that net tensile forces and displacements may ensue, thus eroding the shear resistance of RC columns. A simple procedure is outlined whereby modal analysis may be employed to estimate conservatively vertical earthquake forces on buildings. Finally, areas of further exploration and refinement are identified.     

WHY IS THE MINARET SO SHORT? EVIDENCE FOR EARTHQUAKE DAMAGE ON MT ZION

Abstract

On top of King David's Sepulchre at Mt Zion there is an Ottoman minaret known as al-Nabi Da'ud. Compared with other minarets in Jerusalem, al-Nabi Da'ud seems to be somewhat shorter, and has a squat-like appearance. To track why it is shorter than other minarets, we inspected written historical sources, a sequence of old drawings dated between the mid-eighteenth and mid-nineteenth centuries and analysed the minaret's metric proportions. In drawings dated to and before 1833, the minaret is portrayed much higher than in drawings and photographs dated to and after 1838. Furthermore, comparative height-diameter ratio of various parts of the minaret does not fit those of its counterpart, the al-Qal'a minaret. Thus, we suggest that the minaret was originally built higher but damaged during the 1834 earthquake, and reconstructed to a lower height sometimes afterwards.     

Übersicht der Tätigkeit internationaler Geographenkongresse auf dem Gebiete der Geschichte der Kartographie

Abstract

This paper surveys the career of Benedetto Bordon as a miniaturist, designer of woodcuts, and cartographer. Although from Padua, Bordon worked primarily in Venice where he illuminated religious and classical texts and official ducal documents destined for Venetian noblemen. The writer argues that Bordon designed woodcut illustrations for books printed by Aldus Manutius and others, in addition to the woodcut maps in his 1528 book on islands in the MediteiTanean, Atlantic, and Caribbean. Bordon's lost world map of 1508 is discussed in relation to the map‐making activities of Francesco Rosselli, the Florentine miniaturist and engraver who was in Venice in 1504 and 1508, and in relation to a circle of Venetian scholars and patricians interested in Ptolemy's Cosmographia and in the mapping of the New World.     

NONLINEAR ANALYSIS OF REINFORCED CONCRETE SHEAR WALL UNDER EARTHQUAKE LOADING

A constitutive model for predicting the cyclic response of reinforced concrete structures is proposed. The model adopts the concept of a smeared crack approach with orthogonal fixed cracks and assumes a plane stress condition. Predictions of the model are compared firstly with existing experimental data on shear walls which were tested under monotonic and cyclic loading. The same model is then used in the finite element analysis of a complete shear wall structure which was tested under a large number of cyclic load reversals due to earthquake loading at NUPEC's Tadotsu Engineering Laboratory. Two different finite element approaches were used, namely a two-dimensional and a three-dimensional representation of the test specimen. The ability of the concrete model to -reproduce the most important characteristics of the dynamic behaviour of this type of structural element was evaluated by comparison with available experimental data. The numerical results showed good correlation between the predicted and the actual response, global as well as local response being reasonable close to the experimental one.     

ON THE RESOLUTION OF H/V MEASUREMENTS TO DETERMINE SEDIMENT THICKNESS,A CASE STUDY ACROSS A NORMAL FAULT IN THE LOWER RHINE EMBAYMENT,GERMANY

In recent years, H/V measurements have been increasingly used to map the thickness of sediment fill in sedimentary basins in the context of seismic hazard assessment. This parameter is believed to be an important proxy for the site effects in sedimentary basins (e.g. in the Los Angeles basin). Here we present the results of a test using this approach across an active normal fault in a structurally well known situation. Measurements on a 50 km long profile with 1 km station spacing clearly show a change in the frequency of the fundamental peak of H/V ratios with increasing thickness of the sediment layer in the eastern part of the Lower Rhine Embayment. Subsequently, a section of 10 km length across the Erft-Sprung system, a normal fault with ca. 750 m vertical offset, was measured with a station distance of 100 m. Frequencies of the first and second peaks and the first trough in the H/V spectra are used in a simple resonance model to estimate depths of the bedrock. While the frequency of the first peak shows a large scatter for sediment depths larger than ca. 500 m, the frequency of the first trough follows the changing thickness of the sediments across the fault. The lateral resolution is in the range of the station distance of 100 m. A power law for the depth dependence of the S-wave velocity derived from down hole measurements in an earlier study [Budny, 1984] and power laws inverted from dispersion analysis of micro array measurements [Scherbaum et aL, 2002] agree with the results from the H/V ratios of this study.     

MODELLING OF STRUCTURAL ACCELERATIONS AND APPLICATION TO CONTROLLER DESIGN

In this paper a method for the identification of simplified linear models for building structures is applied to the case when acceleration, rather than displacement, is measured. A frame from benchmark structural controller studies is simulated, and from the input-output data of these simulations, simplified models for the acceleration response of the frame are obtained that have far fewer degrees of freedom. One of these simplified models is used to design a controller, which is tested using an evaluation model from the benchmark controller studies and found to be effective.     

SOIL DAMPING FORMULATION IN NONLINEAR TIME DOMAIN SITE RESPONSE ANALYSIS

Nonlinear time domain site response analysis is used to capture the soil hysteretic response and nonlinearity due to medium and large ground motions. Soil damping is captured primarily through the hysteretic energy dissipating response. Viscous damp-ing, using the Rayleigh damping formulation, is often added to represent damping at very small strains where many soil models are primarily linear. The Rayleigh damping formulation results in frequency dependent damping, in contrast to experiments that show that the damping of soil is mostly frequency independent. Artificially high damp-ing is introduced outside a limited frequency range that filters high frequency ground motion. The extended Rayleigh damping formulation is introduced to reduce the over-damping at high frequencies. The formulation reduces the filtering of high frequency motion content when examining the motion Fourier spectrum. With appropriate choice of frequency range, both formulations provide a similar response when represented by the 5% damped elastic response spectrum.

The proposed formulations used in non-linear site response analysis show that the equivalent linear frequency domain solution commonly used to approximate non-linear site response underestimates surface ground motion within a period range relevant to engineering applications. A new guideline is provided for the use of the proposed formulations in non-linear site response analysis.     

DESIRABLE STRENGTH DISTRIBUTION FOR ASYMMETRIC STRUCTURES WITH STRENGTH-STIFFNESS DEPENDENT ELEMENTS

Recent studies have shown that for many reinforced concrete lateral force-resisting elements (LFRE) stiffness is dependent on strength, and as a result strength assign-ment to these elements would affect both the strength and stiffness distributions in a structure. As a consequence, stiffness distribution cannot be considered known prior to strength assignment. This implies that in assigning strength to LFRE, the designer has the ability not only to prescribe the strength distribution, but also indirectly control the stiffness distribution in the structure. In this paper, a study is made on the seis-mic performance of a number of single-story structures to reconfirm that the “balanced CV-CR location” criterion, previously suggested by the writers, constitutes a desirable strength/stiffness distribution for minimising torsional response of asymmetric reinforced concrete structures.     

汶川地震导致的古建筑震害

为了解汶川地震造成的古建筑震害及对古建筑的保护,根据古建筑震害资料,通过归纳方法,获得了古建筑不同的震害症状：对木结构而言,主要有地基破坏、柱底侧移、柱身倾斜、节点拔榫、装修开裂、梁架歪闪、瓦件掉落、填充墙破坏等;而砖石及砖木结构由于承重材料的抗拉、压、剪强度相对较差,容易产生倒塌等严重震害。在此基础上,通过勘查分析方法,获得了古建筑产生震害的主要原因：地震力过大、古建筑缺乏及时保养与加固、施工原因及砖石材料本身强度差的原因等。针对不同的震害原因,提出了相应的抗震加固建议。在上述工作基础上,得出如下结论：为提高古建筑的抗震性能,应加强对古建筑的维护与加固,及时清除各种隐患,将地震产生的破坏减小到最轻的程度。