ANALISA STATIK DAN DINAMIK GEDUNG BERTINGKAT BANYAK AKIBAT GEMPA BERDASARKAN SNI 1726-2012 DENGAN VARIASI JUMLAH TINGKAT

Diterapkannya SNI 1726-2012 sebagai standar yang baru telah menambah dan mengubah ruang lingkup tata cara perhitungan gempa menjadi lebih luas sehingga dapat mengikuti perkembangan zaman yang ada. Beban gempa dapat dianalisis secara statik maupun dinamik. Untuk analisa statik digunakan metode gaya lateral ekivalen, dan untuk analisa dinamik digunakan metode spektrum respons ragam. Penelitian ini bertujuan untuk membandingkan hasil kedua metode tersebut, sehingga kita dapat mengetahui metode mana yang lebih optimal dalam merencanakan struktur gedung tahan gempa. Struktur gedung yang dimodelkan merupakan gedung beraturan, dengan jumlah tingkat yang divariasikan. Model struktur dibagi kedalam portal 5 tingkat, 10 tingkat, dan 15 tingkat. Penelitian ini menggunakan bantuan program SAP2000 v18 untuk mempermudah proses analisa gempa. Hasil penelitian yang akan dibandingkan adalah displacement antar tingkat dan base shear yang terjadi akibat gaya gempa. Hasil analisa telah menunjukkan bahwa analisa statik mengeluarkan hasil yang lebih besar untuk ketiga model struktur dibandingkan dengan analisa dinamik. Perbedaan displacement antar tingkat yang dihasilkan oleh kedua metode pada ketiga model struktur masih masuk dalam batasan displacement antar tingkat ijin yang disyaratkan dalam SNI 1726-2012, sehingga ketiga model masih bisa dianalisa dengan analisa statik dan analisa dinamik. Karena hasil displacement dan base shear pada analisa statik lebih besar dari analisa dinamik, maka analisa statik lebih aman jika digunakan untuk pembebanan gaya gempa dalam perhitungan struktur secara umum. Walaupun dalam analisa gempa, analisa dinamik merupakan analisa yang lebih akurat karena proses analisa yang lebih mendekati ke keadaan yang sebenarnya. Kata Kunci : SNI 1726-2012, analisa statik, analisa dinamik, SAP200

Evaluasi Perbandingan Benda Uji Berbentuk Hollowbrick Terhadap Silinder

Hollow-brick merupakan elemen bahan bangunan yang digunakan sebagai fungsi dinding dimana keberadaannya hanya sebagai sekat. Berdasarkan bahan pembentuk, hollow-brick memiliki peranan dalam penambah kekakuan lateral suatu bangunan. Penelitian dilakukan untuk mengevaluasi kekuatan tekan terhadap ukuran benda uji hollow-brick. Penelitian menggunakan metode eksperimental di laboratorium berupa pembuatan benda uji hollow-brick, silinder dan kubus dengan variasi campuran yang dibuat adalah 1 Portland Cement (PC) : 4 pasir : 8 abu batu : 0,6 tras, selanjutnya 1 : 5 : 7 : 0,6; 1 : 6 : 6 : 0,6; 1 : 7 : 5 : 0,6; 1 : 8 : 4 : 0,6. Hasil penelitian menunjukan berat volume rata-rata hollow-brick kode campuran VC.2, VC.3, VC.4, VC.5 berturut-turut sebesar 1608 kg/m3, 1593 kg/m3, 1611 kg/m3, 1627 kg/m3. Pemadatan benda uji hollow-brick jauh lebih padat dibandingkan benda uji lain sehingga menghasilkan kuat tekan lebih besar yakni kuat tekan pada umur 28 hari benda uji hollow-brick berkisar 3,39 - 5,10 MPa, silinder berkisar 0,92 – 2,04 MPa, dan kubus berkisar 0,74 – 1,05 MPa. Perbedaan cara pemadatan setiap benda uji menghasilkan beda kuat tekan besar. Persentase kuat tekan hollow-brick terhadap benda uji lain menunjukkan perbedaan yang sangat besar dimana persentase hollow-brick terhadap benda uji silinder umur 28 hari antara 219 – 391% dan persentase hollow-brick terhadap kubus umur 28 hari antara 415 – 538%. Klasifikasi mutu berdasarkan SK SNI S-04-1989-F yaitu menunjukan variasi campuran VC.1 tergolong pada mutu II sebagai tingkat mutu tertinggi dibandingkan variasi campuran VC.3 VC.4 VC.5 tergolong pada mutu III dan VC.2 tergolong pada mutu IV sebagai tingkat mutu terendah

Neogene to Quaternary evolution of carbonate and mixed carbonate-siliciclastic systems along New Caledonia's eastern margin (SW Pacific)

Neogene and Quaternary shallow-water carbonate records surrounding New Caledonia main island, Grande Terre, provide a good example for understanding the stratigraphic architecture of tropical mixed carbonate-siliciclastic systems. Due to a southeastern tilt of the eastern margin, the eastern shelf of Grande Terre has been better preserved from erosion than the western part, favouring the development and preservation of shallow-water carbonates. Based on the integration of bathymetric and seismic data, along with paleoenvironmental and biostratigraphic constraints derived from dredged carbonate rocks, a comprehensive geomorphological and architectural characterization of the offshore eastern margin of Grande Terre has been made. During the Mio-Pliocene, a wide, up to 750 m-thick carbonate build-up developed and extended over at least 350 km from north to south. This Mio-Pliocene build-up, currently lying at 300 to 600 m water depths, is overlain by a Pleistocene-Holocene barrier reef-lagoon complex and associated slope deposits. The switch from aggrading Neogene carbonate banks to backstepping Quaternary platforms likely reflects an increase in accommodation due to a high subsidence rate or to relative sea-level rise, and/or results from a switch in carbonate producers associated with global environmental changes. The internal architecture of the Quaternary barrier reef-lagoon complex is highlighted, especially the development of lowstand siliciclastic prisms alternating with transgressive shallow-water carbonate sequences. This pattern agrees with the reciprocal sedimentation model typically invoked for mixed sedimentary systems. This stratigraphic pattern is well developed in front of the Cap Bayes inlet in the north of our study area, yet it is not observed southward along the eastern margin. This difference suggests that other factors than relative sea-level variations directed the architecture of the margin, such as low terrigenous inputs, lagoon paleo-drainage networks or sediment by-pass towards deep basins

Sedimentological imprint on subseafloor microbial communities in Western Mediterranean Sea Quaternary sediments

An interdisciplinary study was conducted to evaluate the relationship between geological and paleoenvironmental parameters and the bacterial and archaeal community structure of two contrasting subseafloor sites in the Western Mediterranean Sea (Ligurian Sea and Gulf of Lion). Both depositional environments in this area are well-documented from paleoclimatic and paleooceanographic point of views. Available data sets allowed us to calibrate the investigated cores with reference and dated cores previously collected in the same area, and notably correlated to Quaternary climate variations. DNA-based fingerprints showed that the archaeal diversity was composed by one group, Miscellaneous Crenarchaeotic Group (MCG), within the Gulf of Lion sediments and of nine different lineages (dominated by MCG, South African Gold Mine Euryarchaeotal Group (SAGMEG) and <i>Halobacteria</i>) within the Ligurian Sea sediments. Bacterial molecular diversity at both sites revealed mostly the presence of the classes <i>Alphaproteobacteria</i>, <i>Betaproteobacteria</i> and <i>Gammaproteobacteria</i> within <i>Proteobacteria</i> phylum, and also members of <i>Bacteroidetes</i> phylum. The second most abundant lineages were <i>Actinobacteria</i> and <i>Firmicutes</i> at the Gulf of Lion site and <i>Chloroflexi</i> at the Ligurian Sea site. Various substrates and cultivation conditions allowed us to isolate 75 strains belonging to four lineages: <i>Alpha-</i>, <i>Gammaproteobacteria</i>, <i>Firmicutes</i> and <i>Actinobacteria</i>. In molecular surveys, the <i>Betaproteobacteria</i> group was consistently detected in the Ligurian Sea sediments, characterized by a heterolithic facies with numerous turbidites from a deep-sea <i>levee</i>. Analysis of relative betaproteobacterial abundances and turbidite frequency suggested that the microbial diversity was a result of main climatic changes occurring during the last 20 ka. Statistical direct multivariate canonical correspondence analyses (CCA) showed that the availability of electron acceptors and the quality of electron donors (indicated by age) strongly influenced the community structure. In contrast, within the Gulf of Lion core, characterized by a homogeneous lithological structure of upper-slope environment, most detected groups were <i>Bacteroidetes</i> and, to a lesser extent, <i>Betaproteobacteria</i>. At both site, the detection of <i>Betaproteobacteria</i> coincided with increased terrestrial inputs, as confirmed by the geochemical measurements (Si, Sr, Ti and Ca). In the Gulf of Lion, geochemical parameters were also found to drive microbial community composition. Taken together, our data suggest that the palaeoenvironmental history of erosion and deposition recorded in the Western Mediterranean Sea sediments has left its imprint on the sedimentological context for microbial habitability, and then indirectly on structure and composition of the microbial communities during the late Quaternary

Pleistocene Tectono-magmato-volcanic events recorded east of Mayotte - insights for the ongoing seismo-volcanic crisis

The offshore eastern Mayotte area has been extensively studied since the outbreak of the seismo-volcanic crisis in May 2018. Several oceanographic surveys have been carried out by REVOSIMA – https://doi.org/10.18715/MAYOTTE.REVOSIMA (MAYOBS cruises -https://doi.org/10.18142/291) for monitoring purpose, or for academic research (SISMAORE - https://doi.org/10.17600/18001331 and SCRATCH cruises - https://doi.org/10.17600/18002274). They offer a complete coverage of the eastern slope and abyssal plain with multibeam bathymetry and backscatter imagery, sub-bottom profiler (SBP), and several sediment cores. This set of data offers the opportunity to describe the morphology of the area and details the first tens of meters of the sedimentary succession on the abyssal plain.We discover several features including faults, domes and massive chaotic deposits that developed or occurred during Quaternary in the vicinity of the new Fani Maore Volcano. Domes are interpreted as forced folds related to the intrusion of a large sill at depth. The main fault crossing the largest forced fold is a succession of en-echelon segments with vertical throws of up to 8 meters and a preferential N130° strike compatible with the present day regional dextral context. Analysis of the SBP profiles reveals that faulting and doming associated to sill intrusion occurred simultaneously, and together with the deposition of two massive (several km3) and chaotic lobes at the foot of the Mayotte slope. Sediment cores collected over or close to the massive deposits indicate a mixed bioclastic-volcanoclastic content with a large amount of pumices, whose aspect and chemical composition are identical to volcanic edifices located on the upper slope (Horseshoe Volcano) or onshore (Petite-Terre). Backscatter imagery also reveals streaks that cover the lobes and trace back to the same upper slope area. Analysis of bioclasts from a core catcher stopped in the upper part of the deposit shows a large variety of foraminifers, shells fragments, with a little proportion originating from the upper-slope and shelf. We propose that these massive lobe deposits might have occurred as the pumice-dominated material ejected at HV or PT flows downslope, thus reworking and incorporating a substantial amount of hemipelagic deposits along the slope and over the abyssal plain. These observations suggests that a tectono-magmato-volcanic event occurred during recent geological time (Late Pleistocene according to early estimations). At least one comparable set of similar and synchronous features appears on our dataset thus implying the occurrence of a similar event, earlier in the Pleistocene. The correlations between these events and the activity at HV and PT volcanic centers are critical, as it would provide a recurring scenario to compare with present day seismo-volcanic crisis at Mayotte.This work is funded by REVOSIMA, ANR funded COYOTES project, and internal BRGM Project PDEV MAYOTTE.COmores & maYotte : vOlcanisme, TEctonique et Sismicit

Fades associations and geometry of nummulite bodies : example of the Kesra in Central Tunisia (NW Kairouan)

Jorry S., Caline Bruno, Davaud Eric. Fades associations and geometry of nummulite bodies : example of the Kesra in Central Tunisia (NW Kairouan). In: Géologie Méditerranéenne. Tome 28, numéro 1-2, 2001. Anatomy of Carbonate Bodies / Anatomie des corps carbonates. International Meeting / Colloque international. Marseille, 9-12 mai 2001, France, sous la direction de Marc Floquet, Jérôme Hennuy et Jean-Pierre Masse. pp. 103-106

Fades associations and geometry of nummulite bodies : example of the Kesra in Central Tunisia (NW Kairouan)

Jorry S., Caline Bruno, Davaud Eric. Fades associations and geometry of nummulite bodies : example of the Kesra in Central Tunisia (NW Kairouan). In: Géologie Méditerranéenne. Tome 28, numéro 1-2, 2001. Anatomy of Carbonate Bodies / Anatomie des corps carbonates. International Meeting / Colloque international. Marseille, 9-12 mai 2001, France, sous la direction de Marc Floquet, Jérôme Hennuy et Jean-Pierre Masse. pp. 103-106

Controls on the distribution of nummulite facies: a case study from the late Ypresian el Garia formation (Kesra Plateau, Central Tunisia)

Eocene nummulite deposits along the southern Tethys margin locally constitute important hydrocarbon reservoir rocks. In order to understand the heterogeneity of these complex reservoirs, we have carried out a detailed field study of the nummulite limestones which crop out at the Kesra Plateau in Central Tunisia. The main contributions of this paper can be summarised as follows: 1. Various species of Nummulites and planktonic foraminifera were identified in late Ypresian carbonates in the Kesra area and provided accurate biostratigraphic ages. Nummulitic limestones occur in the Chouabine and El Garia Formations representing deposition over a period of about 2Ma. 2. Six depositional facies have been identified in the El Garia Formation, ranging from high-energy nummulitic grainstones to laterally-equivalent lower-energy nummulithoclastic accumulations. Variations in nummulite morphology (size and shape) were used to distinguish a number of subfacies which correspond to different depositional environments. We provide evidence that nummulite accumulations were locally sub-aerially exposed. 3. A 3D reconstruction of the Kesra Plateau outcrop identified two stacked nummulite bodies, deposited under high-energy conditions, which pass laterally into two isolated bodies in more distal parts of the platform. 4. Regional-scale observations indicate that the geometry of the late Ypresian nummulite platform was strongly influenced by the presence of the Oued Bahloul anticline structure, which formed a major environmental barrier between openmarine and more restricted settings. Facies distribution in the Kesra area was strongly controlled by the inherited topography, which reflects the reactivation of NW-SE trending faults during the Late Cretaceous and Paleocene. 5. A tentative 3D facies model illustrates the relationship between facies and fault distributions in the Kesra area. The facies map shows that the best reservoir potential is associated with palaeo-highs, and consists of nummulite limestones deposited in very shallow waters (a few metres) under high-energy conditions