Cost-Benefit Analysis of Alternative Retrofit Strategies for RC Frame Buildings

Monetary losses induced by earthquakes in Reinforced Concrete (RC) buildings are mainly due to damage to non-structural elements (infills, partitions, finishes, etc.). In this study, alternative retrofit strategies for reducing monetary losses in RC frame buildings are examined. They include local strengthening of infills (and partitions) and seismic isolation. The Expected Annual Loss (EAL) of a number of RC frame buildings, pre- and post-rehabilitation, is evaluated, following the time-based assessment approach proposed in the FEMA P-58 guidelines. The breakeven time of each retrofit intervention is then computed, considering the initial cost of the intervention and the expected benefit in terms of EAL reduction.     

Critical Assessment of Intensity Measures for Seismic Response of Italian RC Bridge Portfolios

The seismic assessment of a road network depends largely on the characterization of the fragility of its bridge components. The accuracy of bridge seismic demand estimates and the use of proper intensity measures (IM) will significantly influence such task. The available literature has mainly focused on buildings or a limited number of bridge configurations and IMs, which may not be representative for bridge portfolio assessment studies. In this paper, the correlation quality between a larger pool of traditional and innovative IMs and the nonlinear dynamic response of typical Italian RC bridges is investigated to identify the best-performing IMs.     

Experimental Study of Large Area Suspended Ceilings

Damage of nonstructural components during past seismic events was shown to be not only a critical threat to life safety in extreme cases but also led to substantial reduction of functionality of buildings and other facilities. Because of the complex construction of nonstructural and architectural components, current standards provide only limited guidance for the seismic design. Suspended ceiling systems are among the less understood important nonstructural/architectural components in buildings for which design standards provide limited guidance. To understand the dynamic behavior of suspended ceiling systems, a series of full scale shake table tests of 20 ft × 53 ft and 20 ft × 20 ft ceiling systems were conducted at the Structural Engineering and Earthquake Simulation laboratory (SEESL) at University at Buffalo (UB). For the full scale dynamic testing, a new test frame providing a continuous suspended ceiling area of 1,060 ft² was constructed on the tandem shake tables and was equipped with an open-loop shake table compensation procedure. The combined designs of the physical frame and of the shake table motion controllers allowed simulating the required floor/roof motion according to ICC-ES AC156 standard at the roof of the test structure. Various test configurations were selected in order to determine the influence of different system conditions and the effects or efficiency of various protective systems required by the current standard ASTM E580 for seismic design. Based on the test data and the failure mechanisms observed, damage states are defined, and fragility curves are developed. The results of the fragility analysis show that a ceiling system becomes more vulnerable as (a) it is subjected to multi-directional input motions, (b) heavier tiles are installed, (c) the size of a ceiling area increases, and (d) lateral restraints are not installed. In addition, simplified numerical models that can capture the special behavior of ceiling systems are developed and presented in a companion paper. This paper presents the experimental study of large area suspended ceiling systems involving test setup and configurations, test motions generated by a unique control system, and basic lessons gained from the experiments.     

Mixed Force and Displacement Control for Testing Base-Isolated Bearings in Real-Time Hybrid Simulation

This paper presents a robust mixed force and displacement control strategy for testing of base isolation bearings in real-time hybrid simulation. The mixed-mode control is a critical experimental technique to impose accurate loading conditions on the base isolation bearings. The proposed mixed-mode control strategy consists of loop-shaping and proportional-integral-differential controllers. Following experimental validation, the mixed-mode control was demonstrated through a series of real-time hybrid simulation. The experimental results showed that the developed mixed-mode control enables accurate control of dynamic vertical force on the base isolation bearings during real-time hybrid simulation.     

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.