Expert systems for quality prediction in structural engineering

This work deals with quality level prediction in concrete structures through the helpful assistance of an expert system wich is able to apply reasoning to this field of structural engineering. Evidences, hypotheses and factors related to this human knowledge field have been codified into a Knowledge Base in terms of probabilities for the presence of either hypotheses or evidences,and conditional presence of both. Human experts in structural engineering and safety of structures gave their invaluable knowledge and assistance necessary when constructing the "computer knowledge body".

A framework for adaptive e-learning for continuum mechanics and structural analysis

This paper presents a project for providing the students of Structural Engineering with the flexibility to learn outside classroom schedules. The goal is a framework for adaptive E-learning based on a repository of open educational courseware with a set of basic Structural Engineering concepts and fundamentals. These are paramount for students to expand their technical knowledge and skills in structural analysis and design of tall buildings, arch-type structures as well as bridges. Thus, concepts related to structural behaviour such as linearity, compatibility, stiffness and influence lines have traditionally been elusive for students. The objective is to facilitate the student a teachinglearning process to acquire the necessary intuitive knowledge, cognitive skills and the basis for further technological modules and professional development in this area. As a side effect, the system is expected to help the students improve their preparation for exams on the subject. In this project, a web-based open-source system for studying influence lines on continuous beams is presented. It encompasses a collection of interactive user-friendly applications accessible via Web, written in JavaScript under JQuery and Dygraph Libraries, taking advantage of their efficiency and graphic capabilities. It is performed in both Spanish and English languages. The student is enabled to set the geometric, topologic, boundary and mechanic layout of a continuous beam. While changing the loading and the support conditions, the changes in the beam response prompt on the screen, so that the effects of the several issues involved in structural analysis become apparent. This open interaction with the user allows the student to simulate and virtually infer the structural response. Different levels of complexity can be handled, whereas an ongoing help is at hand for any of them. Students can freely boost their experiential learning on this subject at their own pace, in order to further share, process, generalize and apply the relevant essential concepts of Structural Engineering analysis. Besides, this collection is being added to the "Virtual Lab of Continuum Mechanics" of the UPM, launched in 2013 (http://serviciosgate.upm.es/laboratoriosvirtuales/laboratorios/medios-continuos-en-construcci%C3%B3n)

Integral Bridge for High-Speed Railway

The structural continuity of fully integral bridges entails many advantages and some drawbacks. Among the latter, the cyclic expansions and contractions of the deck caused by seasonal thermal variations impose alternating displacements at the piers and abutments, with effects that may be difficult to establish reliably. The advantages include easier construction and cheaper maintenance but, especially, horizontal loads can be transmitted to the ground in a much better way than in conventional bridges. This paper first presents a methodology for dealing with the problems that the cyclic displacements imposed raise at the abutments and at the bridge piers. At the former, large pressures may develop, possibly accompanied by undesirable surface settlements. At the latter, the degree of cracking and the ability to carry the specified loads may be in question. Having quantified the drawbacks, simplified but realistic analyses are conducted of the response of an integral bridge to braking and seismic loads. It is shown that integral bridges constitute an excellent alternative in the context of the requirements posed by new high-speed railway lines.

Dynamic Response of Wind Turbines to Theoretical 3D Seismic Motions Taking into Account the Rotational Component

We study the dynamic response of a wind turbine structure subjected to theoretical seismic motions, taking into account the rotational component of ground shaking. Models are generated for a shallow moderate crustal earthquake in the Madrid Region (Spain). Synthetic translational and rotational time histories are computed using the Discrete Wavenumber Method, assuming a point source and a horizontal layered earth structure. These are used to analyze the dynamic response of a wind turbine, represented by a simple finite element model. Von Mises stress values at different heights of the tower are used to study the dynamical structural response to a set of synthetic ground motion time histories

Experimental and Analytical Study of Masonry Infill Reinforced Concrete Frames Retrofitted with Steel Braces

In the present work a seismic retrofitting technique is proposed for masonry infilled reinforced concrete frames based on the replacement of infill panels by K-bracing with vertical shear link. The performance of this technique is evaluated through experimental tests. A simplified numerical model for structural damage evaluation is also formulated according to the notions and principles of continuum damage mechanics. The proposed model is calibrated with the experimental results. The experimental results have shown an excellent energy dissipation capacity with the proposed technique. Likewise, the numerical predictions with the proposed model are in good agreement with experimental results.

Discussion of "Simplified Model of Low Cycle Fatigue for RC Frames"

To model strength degradation due to low cycle fatigue, at least three different approaches can be considered. One possibility is based on the formulation of a new free energy function and damage energy release rate, as was proposed by Ju(1989). The second approach uses the notion of bounding surface introduced in cyclic plasticity by Dafalias and Popov (1975). From this concept, some models have been proposed to quantify damage in concrete or RC (Suaris et al. 1990). The model proposed by the author to include fatigue effects is based essentially in Marigo (1985) and can be included in this approach.

QL-CONST1: an expert system for quality level prediction in concrete structures

Current trends in the fields of artifical intelligence and expert systems are moving towards the exciting possibility of reproducing and simulating human expertise and expert behaviour into a knowledge base, coupled with an appropriate, partially ‘intelligent’, computer code. This paper deals with the quality level prediction in concrete structures using the helpful assistance of an expert system, QL-CONST1, which is able to reason about this specific field of structural engineering. Evidence, hypotheses and factors related to this human knowledge field have been codified into a knowledge base. This knowledge base has been prepared in terms of probabilities of the presence of either hypotheses or evidence and the conditional presence of both. Human experts in the fields of structural engineering and the safety of structures gave their invaluable knowledge and assistance to the construction of the knowledge base. Some illustrative examples for, the validation of the expert system behaviour are included.

Influence of the Second Flexural Mode on the Response of High-Speed Bridges

This paper deals with the assessment of the contribution of the second flexural mode to the dynamic behaviour of simply supported railway bridges. Alluding to the works of other authors, it is suggested in some references that the dynamic behaviour of simply supported bridges could be adequately represented taking into account only the contribution of the fundamental flexural mode. On the other hand, the European Rail Research Institute (ERRI) proposes that the second mode should also be included whenever the associated natural frequency is lower than 30 Hz]. This investigation endeavours to clarify the question as much as possible by establishing whether the maximum response of the bridge, in terms of displacements, accelerations and bending moments, can be computed accurately not taking account of the contribution of the second mode. To this end, a dimensionless formulation of the equations of motion of a simply supported beam traversed by a series of equally spaced moving loads is presented. This formulation brings to light the fundamental parameters governing the behaviour of the beam: damping ratio, dimensionless speed $ \alpha$=VT/L, and L/d ratio (L stands for the span of the beam, V for the speed of the train, T represents the fundamental period of the bridge and d symbolises the distance between consecutive loads). Assuming a damping ratio equal to 1%, which is a usual value for prestressed high-speed bridges, a parametric analysis is conducted over realistic ranges of values of $ \alpha$ and L/d. The results can be extended to any simply supported bridge subjected to a train of equally spaced loads in virtue of the so-called Similarity Formulae. The validity of these formulae can be derived from the dimensionless formulation mentioned above. In the parametric analysis the maximum response of the bridge is obtained for one thousand values of speed that cover the range from the fourth resonance of the first mode to the first resonance of the second mode. The response at twenty-one different locations along the span of the beam is compared in order to decide if the maximum can be accurately computed with the sole contribution of the fundamental mode.

A damage model for seismic retrofitting of structures

Numerous damage models have been developed in order to analyse the seismic behavior. Among the different possibilities existing in the literature, it is very clear that models developed along the lines of Continuum Damage Mechanics are more consistent with the definition of damage like a phenomenon with mechanical consequences as they include explicitly the coupling between damage and mechanical behavior. On the other hand, for seismic processes, phenomena such as low cycle fatigue may have a pronounced effect on the overall behavior of the frames and, therefore, its consideration turns out to be very important. However, many of existing models evaluate the damage only as a function of the maximum amplitude of cyclic deformation without considering the number of cycles. In this paper, a generalization of the simplified model proposed by Flórez is made in order to include the low cycle fatigue. Such model employs in its formulation irreversible thermodynamics and internal state variable theory.

Vibrations of Short Span Railway Bridges for High Speed Lines

The physical model based on moving constant loads is widely used for the analysis of railway bridges. Nevertheless, this model is not well-suited for the study of short span bridges (L<=15-20 m), and the results it produces (displacements and accelerations) are much greater than those obtained experimentally. In this paper two factors are analysed which are believed to have an influence in the dynamic behaviour of short bridges. These two factors are not accounted for by the moving loads model and are the following: the distribution of the loads due to the presence of the sleepers and ballast layer, and the train-bridge interaction. Several numerical simulations have been performed in order to decide on their influence, and the results are presented and discussed herein.

Influence of the Second Bending Mode on the Response of High-Speed Bridges at Resonance

This paper deals with the assessment of the contribution of the second bending mode to the dynamic behavior of simply supported railway bridges. Traditionally the contributions of modes higher than the fundamental have been considered of little importance for the computation of the magnitudes of interest to structural engineers (vertical deflections, bending moments, etc.). Starting from the dimensionless equations of motion of a simply supported beam subjected to moving loads, the key parameters governing the dynamic behavior are identified. Then, a parametric study over realistic ranges of values of those parameters is conducted, and the influence of the second mode examined in detail. The main purpose is to decide whether the second mode should be taken into account for the determination of the maximum displacement and acceleration in high-speed bridges. In addition, the reasons that cause the contribution of the second bending mode to be relevant in some situations are highlighted, particularly with regard to the computation of the maximum acceleration.

Extension of Euskalduna Conference Centre and Concert Hall: A Contemporary Application of Irregular Reciprocal Frames

Reciprocal frame structures, formed by a set of self-supported elements in a closed circuit, have long been used since antiquity to cover large spans with small elements. The roof structure of the Euskalduna conference centre and concert hall extension in Bilbao, covering an irregu- lar geometry of 3000 m2 with a maximum span of 45 m, presented an interesting opportunity to revisit the concept and to apply these classical systems. Furthermore, its analysis and develop- ment led to an interesting discussion on reciprocal frames. They showed great sensitivity of these systems to the local modification of a particular element, establishment of irregular load paths, mobilisation of almost the entire sys- tem when locally applying a punctual load and, finally, its large deformability. Besides, reciprocal frames present particular construction complexities and possibilities due to the moderate length of the structural elements, the predominance of shear-only connec- tions and the necessity of the entire system to be completely erected to guarantee its stability. Euskalduna extension, completed in 2012, is one of the largest and a very par- ticular case of irregular reciprocal frame structures built in the world. It shows the formal possibilities and potentiality of reciprocal frames to respond to free and irregular geometries.

Aplicación de algoritmos paramétricos de generación formal en el diseño estructural. La Ópera de Sídney desde una perspectiva contemporánea.

El importante desarrollo tecnológico e industrial surgido especialmente durante la segunda mitad del siglo pasado ha eliminado las históricas limitaciones técnicas en el ámbito de los pro-­? yectos arquitectónicos, desembocando en la situación actual en la que cualquier planteamiento formal puede ser analizado desde un punto de vista estructural, concluyéndose por tanto que ha desaparecido la barrera del análisis en lo que al desarrollo de un proyecto arquitectónico se refiere. En la actualidad, al igual que a finales del siglo XIX, nos encontramos en un periodo de transi-­? ción, y también, como entonces, es la tecnología la que orienta el cambio. No la tecnología de los nuevos materiales (hormigón y acero) como sucedía tras la revolución industrial sino que es la nueva tecnología digital aplicada a los sistemas de diseño, cálculo y fabricación la que están siendo el motor de la actual transformación. Hoy no es tanto el paradigma mecanicista el que prevalece en muchos casos en la concepción de los edificios sino que, nuevos elementos como la tecnología digital integrada está cambiando la forma de diseñar y concebir el entorno cons-­? truido. Ante este contexto cabría plantearse las siguientes cuestiones: ¿Puede el diseño paramétrico y la tecnología CAD-­?CAM-­?CAE en conjunción con los programas actuales de análisis estructural basados en el Método de los Elementos Finitos hacer más sencilla la construcción de estructu-­? ras ligeras y eficientes hoy en día? ¿Puede la tecnología digital ayudar a ampliar el abanico for-­? mal a la hora de diseñar edificios y a la vez permitir el uso de sistemas estructurales racionales que optimicen el consumo de materiales bajo dichas circunstancias?

New Courthouse at El Ejido

The courthouse at El Ejido has a trapezoid floor plan (47 m × 55/26 m) and comprises two distinct volumes that are structurally connected at the basement level and by the footbridges on the upper storeys. A third trapezoid unit featuring a glazed curtain wall facade cantilevers 8 m off the main facade of the front volume. This facade is a structural diaphragm wall, constituted by nine rows of vertical precast concrete members separated by horizontal cast-in-place, self-compacting concrete chords. The location of the courthouse in a seismic area and the small number of horizontal supports for the facade make this wall potentially vulnerable. The high risk, in particular, during construction required careful planning based on a detailed analysis of the interaction between the structure and the ancillary resources used to build it

Finite element code-based modeling of a multi-feature isolation system and passive alleviation of possible inner pounding

The existing seismic isolation systems are based on well-known and accepted physical principles, but they are still having some functional drawbacks. As an attempt of improvement, the Roll-N-Cage (RNC) isolator has been recently proposed. It is designed to achieve a balance in controlling isolator displacement demands and structural accelerations. It provides in a single unit all the necessary functions of vertical rigid support, horizontal flexibility with enhanced stability, resistance to low service loads and minor vibration, and hysteretic energy dissipation characteristics. It is characterized by two unique features that are a self-braking (buffer) and a self-recentering mechanism. This paper presents an advanced representation of the main and unique features of the RNC isolator using an available finite element code called SAP2000. The validity of the obtained SAP2000 model is then checked using experimental, numerical and analytical results. Then, the paper investigates the merits and demerits of activating the built-in buffer mechanism on both structural pounding mitigation and isolation efficiency. The paper addresses the problem of passive alleviation of possible inner pounding within the RNC isolator, which may arise due to the activation of its self-braking mechanism under sever excitations such as near-fault earthquakes. The results show that the obtained finite element code-based model can closely match and accurately predict the overall behavior of the RNC isolator with effectively small errors. Moreover, the inherent buffer mechanism of the RNC isolator could mitigate or even eliminate direct structure-tostructure pounding under severe excitation considering limited septation gaps between adjacent structures. In addition, the increase of inherent hysteretic damping of the RNC isolator can efficiently limit its peak displacement together with the severity of the possibly developed inner pounding and, therefore, alleviate or even eliminate the possibly arising negative effects of the buffer mechanism on the overall RNC-isolated structural responses.