Analysis of the weightiness of site effects on reinforced concrete (RC) building seismic behaviour: The Adra town example (SE Spain)

Abstract

The damage distribution in Adra town (south-eastern Spain) during the 1993 and 1994 Adra earthquakes (5.0 magnitude), that reached a maximum intensity degree of VII (European Macroseismic Scale (EMS scale)), was concentrated mainly in the south-east zone of the town and the most relevant damage occurred in reinforced concrete (RC) buildings with four or five storeys. In order to evaluate the influence of ground condition on RC building behaviour, geological, geomorphological and geophysical surveys were carried out, and a detailed map of ground surface structure was obtained. Short-period microtremor observations were performed in 160 sites on a 100 m × 100 m dimension grid and Nakamura's method was applied in order to determine a distribution map of soil predominant periods. Shorter predominant periods (0.1-0.3 s) were found in mountainous and neighbouring zones and larger periods (greater than 0.5 s) in thicker Holocene alluvial fans. A relationship T = (0.049 ± 0.001)N , where T is the natural period of swaying motion and N is the number of storeys, has been empirically obtained by using microtremor measurements at the top of 38 RC buildings (ranging from 2 to 9 storeys). 1-D simulation of strong motion on different soil conditions and for several typical RC buildings were computed, using the acceleration record in Adra town of the 1993 earthquake. It is noteworthy that all the aforementioned results show the influence of site effects in the degree and distribution of observed building damage. Figure 4. Continuous microtremor measurements for stationarity analysis: (a) tunnel site (hard rock) and (b) beach site (soft soil).Figure 12. An example of the methodology followed to simulate ground and building responses during the 1993 earthquake in Adra: (a) E-W component of strong motion record in Adra town; (b) simulated strong motion on sediment soil site with a thickness of 30 m (Case 2); (c)-(e) simulated strong motions at the top of buildings with four, six and eight storeys, respectively; and (f) amplitude spectra of the previous strong motions.

Empirical estimates of dynamic parameters on a large set of European buildings

“…For European buildings, our result is strikingly similar to that obtained by Navarro et al (2007) for Spanish RC buildings, who proposed the relationship T = 0.049N, with N equal to the number of floors (assuming 3 m as the inter-storey height). We compared our relationship also with the provisions of EC8 (Fig.…”

“…The height-period relationship we determined is robust and very similar to another relationship proposed for Southern European buildings by Navarro et al (2007). Confirming the results of Gallipoli et al (2008), who analysed a first subset of our data set, we found that our relationship is very different from European code provisions (EC8).…”

“…This resonance approach was used to study the damage pattern of past earthquakes, see e.g. Mucciarelli and Monachesi (1999) for the 1998 Bovec earthquake, Parolai et al (2005) for the 1978 Thessaloniki earthquake, Navarro et al (2007) for the [1993][1994] Adra earthquake. The search for resonance has been recently introduced in microzonation studies of cities such as Granada (Spain, Navarro et al 2004), Senigallia (Italy, Mucciarelli and Tiberi 2007).…”

Current uses of ground penetrating radar in groundwater-dependent ecosystems research

“…3; Fig. 6a) is occupied by Pleistocene colluvials and Pliocene marine terraces over the Precambrian low-permeability metapelitic bedrock (Navarro et al, 2007). Coarse-grained marine terraces form a discontinuous confined perched aquifer from which diffuse discharge contributes to local streams supporting GDE .…”

“…3; Fig. 4a) is located in the discharge area of the Adra River delta (ARD hereafter), a regional aquifer of 60 m in thickness composed of Holocene alluvial and fluvial formations, Pleistocene colluvials, Pliocene marine terraces, and Miocene calcarenites over a Precambrian low-permeability crystalline (metapelitic) bedrock (Navarro et al, 2007). Plio-Quaternary formations discharge to the sea and GDE .…”