Design Principles for Minimum Torsional Response of Wall-Frame Concrete Structures

A seismic design procedure is described incorporating the well-accepted property that the stiffness of reinforced concrete elements is strength dependent and the requirement that the method of assigning strength to elements should be aiming at minimum torsional phenomena. Such a response allows a direct comparison with the findings of a static nonlinear analysis, which may provide the limits of story drifts and the induced plastic rotations in potential plastic hinges. The requirement of a practically translational response implies that the element strength assignment should be based on planar considerations and the initially elastic response should be of minimum torsion.     

Investigation of the Optimum Height of Railway Embankments during Earthquake Based on Their Stability in Liquefaction

One of the most reported problems in the railway embankments is loss of their overall stability and major settlements due to liquefaction. Although several studies have been made on the stabilization of embankments, the effects of the influencing parameters on the stability of embankments during liquefaction have not been sufficiently investigated. The series of two dimensional plane strain finite element (FE) models were developed using multi yield surface plasticity model namely Prevost. The results were represented and discussed in terms of foundation excess pore pressure, embankment settlements and their failure modes. By analyzing the results, the optimum height of embankment which minimizes the settlement and failure cracks was derived.     

The Utility of Discourse Analysis to Heritage Studies: The Burra Charter and Social Inclusion

This paper reviews the methodological utility of Critical Discourse Analysis (CDA) in heritage studies. Using the Burra Charter as a case study we argue that the way we talk, write and otherwise represent heritage both constitutes and is constituted by the operation of a dominant discourse. In identifying the discursive construction of heritage, the paper argues we may reveal competing and conflicting discourses and the power relations that underpin the power/knowledge relations between expertise and community interests. This identification presents an opportunity for the resolution of conflicts and ambiguities in the pursuit of equitable dialogues and social inclusion.     

Seismic Hazard Assessment of the NW Himalayan Fold-and-Thrust Belt,Pakistan, Using Probabilistic Approach

The Seismic Hazard Assessment (SHA) based on probabilistic approach has been carried out for the entire seismically active NW Himalayan Fold and Thrust Belt in Pakistan. Additional information in the form of earthquake catalog, delineation of 41 active faults in a structural map, their relationship to the seismicity, and establishment of seismotectonic zones has also been undertaken.

From the distribution of the 813 events within the study area, it appears that seismicity (≥4.0 M_w) is associated with both surface and blind faults. The clustering of events in specific parts along the surface faults shows that some fault segments, especially in the hinterland zone, are more active. In parts of the active deformational front, like the Salt Range, southern Potwar and Bannu, lesser seismic activity (≥4.0 M_w) could be due to damping effect of the thick Precambrian salt.

A majority of the earthquakes (86%) range in magnitude from 4.0 to 4.9 M_w, followed by 107 events (13%) ranging from 5.0 to 5.9 M_w. The remaining 1% range from 6.0 to 6.7 M_w. There is a predominance of shallow seismicity (<50 km focal depth). Larger magnitudes events are more in the hinterland zone. In contrast, based on distribution of 683 (≥4.0 M_w) events, a deeper level of seismicity (50 to 200 km) prevails especially in the adjoining Hindukush Range of Afghanistan.

Four seismotectonic zones have been established in the area. The b value is highest for the Peshawar-Hazara Seismic Zone (PHSZ) at 1.27, followed by 1.12 for the Surghar-Kurram Seismic Zone (SKSZ). The Swat-Astor Seismic Zone (SASZ) and Kohat-Potwar-Salt Range Seismic Zone (KPSZ) have b values of 0.99 and 1.03, respectively, thereby indicating the occurrence of more events of relatively higher magnitude as compared to the other two zones. The mean activity rate of the earthquakes (λ) ranges from 4.26 to 1.73. In decreasing order, the values are 4.26, 2.62, 2.07, and 1.73 for PHSZ, SASZ, KPSZ, and SKSZ, respectively. Using four regression relationships, the maximum potential magnitude (m₁) has been determined for the 4 Quaternary faults. The highest value within each seismic zone represents its m₁. Our calculations show that m₁ is 7.8 in the hinterland (SASZ and PHSZ) and 7.4 in the foreland part (KPSZ and SKSZ).

SHA, incorporating probabilistic approach, has been undertaken at 10 sites, along with disaggregation at the assigned amplitude of 0.2g. Pakistan does not have an attenuation equation of its own. The two equations of Ambraseys et al. (1996) Ambraseys, N. N., Simpson, K. A. and Bommer, J. J. 1996. Prediction of horizontal response spectra in Europe. Earthquake Engineering and Structural Dynamics, 25: 371–400. [Crossref], [Web of Science ®] , [Google Scholar] and Boore et al. (1997) Boore, D. M., Joyner, W. B. and Fumal, T. E. 1997. Equations from estimating horizontal response spectra and peak acceleration from western North American earthquakes: a summary of recent work. Seismological Research Letters, 68: 128–153. [Crossref] , [Google Scholar] have been used and the results obtained using the equation of Boore et al. (1997) Boore, D. M., Joyner, W. B. and Fumal, T. E. 1997. Equations from estimating horizontal response spectra and peak acceleration from western North American earthquakes: a summary of recent work. Seismological Research Letters, 68: 128–153. [Crossref] , [Google Scholar] have been preferred. In the Probabilistic seismic hazard assessment (PSHA), the PGA values with 10% probability of exceedance in the 50 years, i.e., the return period of 475, have been determined using the EZ-FRISK (6.2 beta version) software. Best-estimated seismic hazard parameters (λ, m₁, m₀, and the β value) of the four seismic zones were used as the input. Results were generated in the form of total hazard curves. Values obtained range from 0.08g (for Bannu) to 0.21g (for Malakand and Kohat). For the other seven sites they are: Astore (0.082g), Kaghan (0.12g), Muzaffarabad (0.13g), Islamabad and Peshawar (0.15g), Talagang (0.16g), and Mangla (0.18g). High population density and more poorly constructed structures in Rawalpindi (twin city of Islamabad) and Peshawar make them more hazardous.     

Site Effects Analyses in the Old City Center of Trieste (NE Italy) Using Accelerometric Data

The influence of local geology and soil conditions on the intensity and the amplification of ground shaking are well known. Part of the old city center of Trieste is built on the site of a former salina, placed at a river mouth and is characterized by soft sediments several tens of meters thick. A new accelerometric station has been recently installed in a historical building, in order to analyse earthquake-induced site amplifications. This station has recorded five regional earthquakes and the related records are compared to those obtained at a nearby bedrock-installed accelerometeric station. Fourier and response spectra for all components are computed and both the H/V ratio and the reference station techniques are used to assess site effects. Noise measurements performed in the historical building, where the accelerometer is located, confirm these results. Relevant amplifications are detected in the frequency range of 2–4 Hz, particularly important for the type of buildings present in this part of the city.     

Effect of SMA Braces in a Steel Frame Building

Pull-back and shaking table test results on a simple model of a three-storey structure that includes shape memory alloys (SMA) copper-based dampers are presented and discussed. The model corresponds to a rigid-framed steel structure and the dampers to austenite CuAlBe wires inserted as bracing at each story. The inclusion of the dissipators in the structure increases the percentage of critical damping from 0.59% for the bare case to 5.95% for the braced system. At the same time, the structural stiffness increases making the first fundamental frequency change from 2.5–3.7 Hz (0.4–0.27s). The net effect of these two factors is a 30–60% reduction of peak relative displacements compared to the ones obtained without dissipation devices when the structure is subjected to earthquake records. Depending on records frequency contents, a reduction of the peak accelerations to near 58% also can be obtained. Additionally, a crude nonlinear analytical model has been studied that can predict the earthquake responses reasonably well.     

Experimental Study of a Structure Under Stress Pulse Simulating Vertical Ground Motion

This article is an attempt to study the effects of a stress pulse simulating strong vertical excitation, particularly at the first steps of the mode of propagation. The structural model represents a two-story single column, having two pairs of cantilever beams on either side. The study is carried out by means of the experimental method of caustics. The areas of maximum stress concentration, as well as the wave front direction within the horizontal elements of the structure, are determined. The influence of the wave and the reflected effects on the top of the column are also studied. The experimental results are compared with the corresponding results obtained by finite element analysis. The results could be used for the development of rules for the effects of the vertical component.     

Shear Modulus and Damping Ratio of Cohesive Soils

This article presents results from a laboratory investigation into the dynamic characteristics of reconstituted and undisturbed cohesive soils by means of resonant-column tests. In particular, results showing the influence of various soil parameters, such as confining stress, overconsolidation ratio, void ratio, plasticity index, calcium carbonate content, and time of confinement on shear modulus and damping ratio at small and high shear strains are presented and then discussed. Relationships for the small-strain shear modulus, the degradation of shear modulus at high strains, and the increase of damping ratio at high strains over its small-strain value are proposed. Finally, the practical implications of the results in the context of seismic site response analysis are discussed.     

Effects of Vertical Load,Strain Rate and Cycling on the Response of Lead-Rubber Seismic Isolators

Lead-rubber isolators represent a valid and economic solution for the seismic isolation of bridge structures and modern manufacturing techniques make available large devices. Velocity effects on small to medium-scale isolators have been discussed by several authors (e.g., Clark et al., 1997 Clark, P. W., Aiken, I. D. and Kelly, J. M. 1997. Experimental studies of the ultimate behavior of seismically isolated structures, Berkeley, CA: Earthquake Engineering Research Center, University of California. Report No. UCB/EERC-97/18 [Google Scholar]; Thompson et al., 2000 Thomson, A. C., Whittaker, A. S., Fenves, G. L. and Mahin, S. A. 2000. “Property modification factors for elastomeric seismic isolation bearings”. In Proceedings of the 12th World Conference on Earthquake Engineering, New Zealand: Auckand. January [Google Scholar]) as well as included in reports of experimental programs (e.g., CERF, 1999 CERF. Civil Engineering Research Foundation, Summary of evaluation findings for the testing of seismic isolation and energy dissipation devices. CERF Report No. 40404. 1999.  [Google Scholar]). Only recently, however, the behavior of large devices was validated under full-scale displacements, loads, and velocities.

In this article, results obtained from an experimental investigation on the effects of axial load and strain rate on the performance of a full-scale lead-core elastomeric bearing for bridge applications, are reported. The bearing response was analyzed with particular attention to the variation of critical performance characteristics in order to produce a set of information that could be implemented in a physically motivated numerical model.

The results, in line with additional tests performed on similar full-scale bearings at the Caltrans SRMD Testing Facility at the University of California San Diego, indicate a moderate effect of the applied vertical load but a significant effect of the strain rate and cycling on all the significant response parameters. This information should be taken into account by designers, particularly when high component of velocities are associated with the expected seismic motion. A simplified numerical model is proposed for the assessment of lead-rubber bearing performance.