Structural Engineering

Nonlinear Analysis of Large Concrete Structures using a Finite Element Shell Model

by Viktor Sigrist

co-authored with Jens Wasner

published in the Proceedings of the 4th International Conference SEMC 2010, 6.-8. Sept. 2010, Cape Town, South Africa.

A new tension stiffening approach for structural concrete is presented and applied to flexural members. Cracking and... more A new tension stiffening approach for structural concrete is presented and applied to flexural members. Cracking and deformation behaviour in the tension zone is accounted for with eference to the Tension Chord Model. With the choice of tensile and residual concrete strength values the interaction between
concrete and reinforcement as well as the influences of hrinkage restraint and random strength distribution can be considered. The proposed model is compared to test results of two-span slab strips.

Nuclear Power Plant Structural Safety

by Martin Berka

ATENA Latest Newsletter, March 2012

by Martin Berka

Modelling shell structures with ATENA

by Martin Berka

Nuclear Containment Cracking Analysis

by Martin Berka

SARA

by Martin Berka

ATENA Tunnels

by Martin Berka

ATENA Analysis of Bridges Structures

by Martin Berka

ATENA specification analysis

by Martin Berka

ATENA products features

by Martin Berka

ATENA 3D Engineering features

by Martin Berka

ATENA Science features

by Martin Berka

Plastic Design of Steel-concrete Composite Girder Bridges

by Árpád Rózsás

Master of Science Thesis

The primary purpose of this thesis is to investigate the plastic reserve of composite plate girder bridges. These... more The primary purpose of this thesis is to investigate the plastic reserve of composite plate girder bridges. These structures are suitable for this due to the synergetic combination of the concrete and steel. The former provides the “cheap” stiffness and strength in compression while the steel in tension ensures the ductility. However, the theoretical and experimental aspects of plastic design are well established only in the US provisions are available for the designers.

The aim was to inquiry the plastic design in the framework of the Eurocode through an existing elastically designed bridge. In the first part of the study the necessary theoretical background is overviewed, the related literature is examined. The main emphasis is placed on the ultimate load bearing capacity, which is determined using various limit states, such as first hinge, incremental collapse and plastic collapse. The safety levels of these limit states were also investigated. To ensure the ductility of the pier-sections innovative structural solutions gathered and evaluated. The selected bridge is a composite, plate girder, continuous structure formed by three spans (30,0-40,0-30,0m). This was redesigned following plastic principles, the relevant provisions and the findings of the researchers.

The calculations showed that − for the original structure − the traffic load could be increased by ~30 and ~60% over the first yield in case of using first hinge and shakedown limit states, respectively. It was found that the safety levels of these limit states at least reach or exceed that of the first yield or first hinge. It should be noted that these results reflect only one example; nevertheless, they are in good agreement with the American results. The redesign yielded to a structure with cleaner lines with considerably less section transition and about 25% structural steel saving. Based on the calculations and international data the plastic design of girder bridges appears to be a promising way, at the same time more research required.

Scalar and vector time series methods for vibration based damage diagnosis in a scale aircraft skeleton structure

by Fotis Kopsaftopoulos

invited paper to Journal of Theoretical and Applied Mechanics, Vol. 49, No. 3, 2011.

Vibration based health monitoring for a lightweight truss structure: experimental assessment of several statistical time series methods

by Fotis Kopsaftopoulos

Mechanical Systems and Signal Processing (ISMA Special Issue), Vol. 24, pp. 1977-1997, 2010.

Output-Only Parametric Identification of a Scale Cable-Stayed Bridge Structure: a comparison of vector AR and stochastic subspace methods

by Fotis Kopsaftopoulos

Proceedings of the 4th International Operational Modal Analysis Conference (IOMAC), Istanbul, Turkey, 9-11 May 2011.

Back - analysis sheds light on the history of the Acropolis Wall: The interpretation of a permanent structural failure

by Dimitris Egglezos

Co-authored with D. Moullou, published in XV ECSMGE European Conference

This work describes a back-analysis for the interpretation of a serious structural failure observed in an area of the... more This work describes a back-analysis for the interpretation of a serious structural failure observed in an area of the Acropolis North Circuit Wall. The failure occurred, according to the available historical and archaeological evidence, at the end of the 18th or beginning of the 19th century and it includes a) the collapse of the upper part of the Wall in the area examined (the crown of the Wall that had been constructed of architectural members of the entablature of the Old Temple of Athena), b) significant out-ward lean from the vertical (7 cm) of the remaining lower part (the part beneath the crown that collapsed), c) rotation of approx-imately 1o d) systematic cracking of the outward face of the wall. For the analysis, the principles of rock mechanics were applied for simulation of the dry-masonry construction. Since the damage was primarily attributed to a strong earthquake motion, for the problem description information is drawn from a wide range of scientific specialization. The analyses comprised: 2-D FE elas-toplastic analysis, simplified (pseudostatic) spectral dynamic analysis and a rigorous 2-D time history analysis. The results are proven very satisfactory. Τhe permanent displacement of the current crown of the wall, the rotation of the structure, the collapse of the entablature members (form Γ) and the systematic net of fractures at the outward side of the wall are consistently predicted. Therefore, the assumption that the damage was caused by an earthquake was also verified, limiting the termini of the event be-tween 1785 and 1805.

In-situ tests on the Parthenon columns for the assessment of their foundation condition

by Dimitris Egglezos

Co- authored with E.E. Toumbakari, published in XV ECSMGE European Conference, Athens 2011

The paper reports a) the in-situ trial load tests, which were carried out on the four, out of six, columns of the... more The paper reports a) the in-situ trial load tests, which were carried out on the four, out of six, columns of the Parthenon western side, the Opisthodomos, during the recent restoration project (2001-2004) and b) the analytical assessment of their structural res-ponse, including foundation, based on the obtained experimental data.The dismantling of the entablature members during the anastylosis project, gave the opportunity for the performance of in situ trial load tests in order to study the response of the co-lumns, interacting to their foundation. The testing project consisted of the application of a horizontal force of 10-11kN at the ca-pital of each column. At the same time, the horizontal displacement of the capital and the vertical displacement of the base marble block, were measured The test was carried out twice in each direction, to account for differences in the foundation condi-tions. For the evaluation and the interpretation of the test results a back-analysis was performed. For the (3-d nonlinear elastic) analysis Rock-Mechanics principles were applied. The idea is that dry masonry structure, from natural rock stone blocks connec-ted with frictional “joint” forces are analogous to a jointed rockmass system. The comparison of measured values and analytical predictions are generally in good agreement, offering increased accuracy.According to the results, discrete modelling with pro-perly determined parameters for monument‟s geomaterials can satisfactorily be applied to restoration analyses of this type of structure and could form the base for more complex calculations involving dynamic effects e.g. earthquake.

Effects of actuator tuning on pseudo-dynamic tests

by Quincy Ma

Presented at the Ninth Pacific Conference on Earthquake Engineering. Co-authored with John O'Hagan

Experimental error is an unavoidable feature of all experimental investigations. The effects of this on the accuracy... more Experimental error is an unavoidable feature of all experimental investigations. The effects of this on the accuracy of pseudo-dynamic (PSD) testing have been the subject of many studies but it remains not well understood and it has been rarely validated experimentally. An important consideration when investigating experimental errors in PSD tests is the performance of the actuator. In general, the actuator motion will lag the displacement command. It is important to acknowledge this delay in the PSD algorithm to ensure correct restoring forces are measured. Incorrect restoring force arising from systematic measurement errors can propagate through the PSD solution process and invalidate the results. This paper reports on a series of experiments assessing the optimum wait time for a default tuned actuator to established a stabilised feedback value for PSD tests. Force feedbacks were intentionally measured prematurely to quantify the error propagation in the algorithm. It was experimentally shown that errors of this kind did not significantly alter the time history response for a harmonically excited SDOF system with damping. The results showed that a constant hold time is not practical as actuator lag time can vary dramatically. It is recommended that actuator displacement is checked iteratively within each load step to ensure the command displacement is achieved before feedback values are measured. This would reduce systematic error and in turns minimise numerical damping in the PSD algorithm.

Earthquake performance assessment and rehabilitation of two historical unreinforced masonry buildings

by Ufuk Hancilar

Ufuk Hancilar · Eser Çaktı · Mustafa Erdik

Abstract: The paper describes the earthquake performance assessment of two historical
buildings located in... more Abstract: The paper describes the earthquake performance assessment of two historical
buildings located in Istanbul exposed to a Mw = 7+ earthquake expected to hit the city and
proposes solutions for their structural rehabilitation and/or strengthening. Both buildings
are unreinforced clay brick masonry (URM) structures built in 1869 and 1885, respectively.
The first building is a rectangular-shaped structure rising on four floors. The second one
is L-shaped with one basement and three normal floors above ground. They survived the
1894, Ms = 7.0 Istanbul Earthquake, during which widespread damage to URM buildings
took place in the city. Earthquake ground motion to be used in performance assessment and
retrofit design is determined through probabilistic and deterministic seismic hazard assessment.
Strength characteristics of the brick walls are assessed on the basis of Schmidt hammer
test results and information reported in the literature. Dynamic properties of the buildings
(fundamental vibration periods) are measured via ambient vibration tests. The buildings
are modelled and analyzed as three-dimensional assembly of finite elements. Following the
preliminary assessment based on the equivalent earthquake loads method, the dynamic analysis
procedure of FEMA 356 (Pre-standard and commentary for the seismic rehabilitation of
buildings, American Society of Civil Engineers, Reston, 2000) and ASCE/SEI 41-06 (Seismic
rehabilitation of existing buildings, American Society of Civil Engineers, Reston, 2007)
is followed to obtain dynamic structural response of the buildings and to evaluate their earthquake
performance. In order to improve earthquake resistance of the buildings, reinforced
cement jacketing of the main load carrying walls and application of fiber reinforced polymer
bands to the secondary walls are proposed.