Bodenverflüssigung bei Erdbeben — Rechnerischer Nachweis mit Lasteinwirkung und Bodenwiderständen

Immer wieder entstehen Erdbeben mit erheblichen Personen‐ und Sachschäden. Immer wieder entfestigen sich dabei sandige Gründungsböden infolge einer Bodenverflüssigung durch die Erdbebenerschütterungen insbesondere bei hohen Grundwasserständen. Selbst solide Bauwerke können in den Untergrund einbrechen, auch wenn sie zuvor über Jahre praktisch setzungsfrei gewesen sind. Das Versagen des Untergrundes durch Bodenverflüssigung ist weltweit als “Liquefaktion‐Effekt” bekannt, wird aber in der täglichen Praxis mitunter immer noch unsicher behandelt. Nachfolgend wird die Mechanik der Lasteinwirkung und der Bodenwiderstände bei einer Erdbebenerschütterung beschrieben und das für baupraktische Berechnungen derzeit gängige Formelwerk dazu zusammengestellt. Damit lässt sich in geeigneter Weise prüfen, ob bei bestimmten Bodenverhältnissen und einem bestimmten Bemessungserdbeben eine Verflüssigung des Untergrundes zu besorgen ist oder ob bauliche Sicherungsmaßnahmen erforderlich sind. Liquefaction due to earthquakes — structural analysis with load actions and soil resistances. Again and again earthquakes have caused severe personal injuries and damages to property. In case of ground motion sandy subsoils especially in connection with high ground water tables can loose their strength and liquify. Then even solid structures may suffer severe settlements and collaps, even though through many years practically no settlements were noticed. This failure mechanism all over the world is wellknow as ”liquefaction”, but in daily practice is still handled with some uncertainness. In the following the mechanism of the load actions and the soil resistances during earthquakes will be described and the nowadays common formulas for the structural analyses will be compiled, enabling the assessment, if certain soil conditions will resist a design earthquake without liquefaction or if structural measures will be required.     

Studies on Hydrotalcite‐Catalyzed Synthesis of Poly(ethylene terephthalate)

Summary: The hydrotalcite‐catalyzed synthesis of PET was studied to clarify the effect of hydrotalcite properties on its catalytic activity. Hydrotalcite was modified by various treatments to tune its activity as a polycondensation catalyst. Hydrotalcite activity was found to decrease upon calcination. However, rehydration of the calcinated hydrotalcite resumed the catalytic activity. The hydrotalcite activity depends on the ratio of magnesium to aluminum cations in its composition, and highest activity occurs at a molar ratio of 2:1. Replacement of the carbonate anions of hydrotalcite by more nucleophilic ones like hydroxide and alkoxide groups resulted in improved catalytic activity. Hydrotalcite has two assembly orders: primary lamination of sheets into plates and secondary agglomeration of plates into particles. Hydrotalcite with larger sheet size showed lower activity. On the other hand, milling of hydrotalcite particles did not affect its activity as it probably enters the reaction on a plate level, which is not affected by milling. Polycondensation resulted in expansion of the hydrotalcite sheets under the effect of formed polymer. Reuse of hydrotalcite after polycondensation followed by depolycondensation resulted in a large activity enhancement.

High‐resolution SEM micrograph of calcinated HT after rehydration.     

Template-assisted large-scale ordered arrays of ZnO pillars for optical and piezoelectric applications

Spatially separated ZnO pillars, typically 300 nm in diameter and 2 microm in height, are fabricated via a template-directed approach that leads to long-range hexagonal order. The templates of Au nanodisk arrays are obtained by using metal membranes as a lithography mask. The growth of ZnO pillars is performed in a double-tube system through vapor diffusion-deposition. The growth mechanism of the pillars is studied in detail and is proposed to be a combination of vapor-liquid-solid and vapor-solid models. The piezoelectric and optical properties of single pillars are characterized using piezoresponse force microscopy and micro-photoluminescence spectroscopy, respectively. The pillars show strong excitonic emissions up to room temperature, which indicate a relatively low defect density and good crystalline quality. The obtained piezoelectric coefficient d(33) is (7.5+/-0.6) pm V(-1), which is to our knowledge the first reported value for a single nanopillar.     

Vergleichender Einsatz von Kohlendioxid und Helium als Gastracer bei der Bodenluftabsaugung

Beim Einsatz von Kohlendioxid (CO ₂ ) als Gastracer im Rahmen von früher durchgeführten Untersuchungen zur Bestimmung pneumatischer Parameter der unges?ttigten Bodenzone im Bereich von Bodenluftabsauganlagen ergaben sich h?ufig unbefriedigende Wiedererhalte von unter 70% der ursprünglich eingebenden Tracermenge. Zur überprüfung der Eignung von CO ₂ wurden deshalb kombinierte CO ₂ -He-Gastracerversuche durchgeführt. Anhand der gewonnenen Versuchsergebnisse kann gezeigt werden, da? sich CO ₂ und ⁴ He trotz unterschiedlicher physiko-chemischer Eigenschaften in der unges?ttigten Zone sehr ?hnlich verhalten. Aufgrund des einfacheren Handlings ist dem CO ₂ als Gastracer sogar in vielen F?llen der Vorzug zu geben.

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While using CO ₂ as gas tracer for estimating the pneumatic parameters of the unsaturated zone in the range of soil vapor extraction wells the recoveries often have been less than 70% of the originally injected tracer amount. To check the applicability of CO ₂ for this purpose combined CO ₂ -Helium gas tracer experiments were conducted. With the results of the experiments it was possible to show that in spite of different physical and chemical properties CO ₂ and Helium behave quite similar in the unsaturated zone. Because CO ₂ is easier to handle, it may be the preferable tracer.

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Eingang des Beitrages: 22.07.96 / Eingang des überarbeiteten Beitrages: 23.12.96     

Structural analysis for tunnels exposed to fire temperatures

Elimination of fire hazards in tunnels is becoming an increasingly important part of tunnel design. Hence, there is a need to understand the response of the tunnel structures to temperatures created by fire inside the tunnel. This paper studies the deformations and stresses of steel linings dimensioned for ground forces, which are additionally exposed to non-uniform high-temperature distributions. The ground-structure interaction and the temperature-induced loss of structural stiffness are considered. Results for a standard fire are presented in diagrams that show the main features and their dependence on important practical parameters.     

Cetuximab inhibits thymidylate synthase in colorectal cells expressing epidermal growth factor receptor

The monoclonal antibody cetuximab directed against the epidermal growth factor receptor (EGFR) is an attractive agent for targeted therapy in advanced colorectal cancer (CRC), especially when combined with 5-fluorouracil (5-FU)-based chemotherapy. However, the mechanisms of cetuximab activity as chemosensitizer remain poorly understood. Using proteome-fluorescence-based technology, we found that cetuximab is able to suppress the expression of thymidylate synthase (TS), which is involved in the mechanism of 5-FU action. Caco-2, HRT-18, HT-29, WiDr and SW-480 CRC cells were found to express EGFR. SW-620 was used as EGFR-negative cell line. Only in EGFR-expressing cells cetuximab is able to inhibit TS expression. Combined treatment with cetuximab and 5-FU revealed a synergistic anti-tumor response that is closely correlated with functional activity of EGFR/mitogen-activated protein kinase (MAPK) pathway. Moreover, no correlation was seen between constitutive TS protein expression, level of cetuximab-induced TS down-regulation and response either to 5-FU alone or in combination with cetuximab. We demonstrated that only EGFR expression with high functional activity of EGFR/MAPK pathway is important for the synergistic effects between cetuximab and 5-FU in the investigated cell lines.     

Analysis of a rough plane pad bearing of finite width

The paper describes the results of a numerical study concerning the effect of two-sided roughness in a finite width slider bearing. The analysis is based upon the assumption that Reynolds equation holds in the presence of roughness and uses Christensen's stochastic models as extended to two-sided roughness. Detailed results for various bearing characteristics as a function of width/length and film thickness ratio show that these parameters have a strong influence on the bearing behaviour.     

Geology explorer: virtual geologic mapping and interpretation

We are developing internet-based freeware for virtual mapping and geologic interpretation. This takes the form of a synthetic, virtual world, Planet Oit, where students are given the means and the equipment to carry out geologic investigation and interpretation as a geologist would in the field. The environment is designed to give students an authentic experience that includes elements of: (1) exploration of a spatially oriented, virtual, world; (2) practical, field oriented, expedition planning and decision-making; and (3) scientific problem solving (i.e. a “hands on” approach to mapping, geologic investigation, data acquisition, and interpretation). The game-like environment is networked, multi-player, and simulation-based. Planet Oit can be visited on the Internet at http://oit.cs.ndsu.nodak.edu/