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In this paper, an experimental investigation is presented on semi-rigid interior beam-to-column connections constituted by precast concrete beams supported on precast concrete column corbels and bending continuity reinforcement bars for bending negative moments. The main purpose of this paper was to analyze the influence of vertical interface grout filling between the corbel and the beam and the position of the bending continuity reinforcement bars (crossing only the column or crossing only the slab) on the behavior of this type of connection. Tests on eight specimens were performed. It was noticed that the vertical interface grout filling contributed to increase both rotational flexural stiffness and flexural strength capacity of the connections when compared to the connections without grout filling. It was also noticed that in the specimens in which the continuity bars crossed only the column, the rotational flexural stiffness was higher. For these last ones, coefficients k and β for predicting the secant stiffness by simplified expression present in Brazilian Code NBR 9062 were evaluate from experimental results. These evaluated coefficients may be regarded as indicative values for structural designers and helpful for future researches. Resumo Neste trabalho apresenta-se um estudo experimental de ligação viga-pilar semirrígida de pilar intermediário constituída de vigas de concreto pré-moldadas apoiadas em consolos de concreto pré-moldado, com presença de armaduras de continuidade resistentes ao momento fletor negativo. O presente trabalho teve como objetivo principal verificar a influência do preenchimento de graute na interface vertical entre o consolo e a viga e a posição da armadura de continuidade (passante somente no pilar e passante somente nas lajes). Foram ensaiados no total oito protótipos. Verificou-se que o preenchimento de graute na interface vertical consolo-viga contribuiu para aumentar tanto a rigidez e quanto a resistência da ligação à flexão quando à comparada a ligação sem o preenchimento desse graute. Verificou-se também que nos protótipos em que as armaduras de continuidade passaram somente no pilar a rigidez à flexão da ligação foi maior. Para estas tipologias de ligação, foram obtidos, a partir dos resultados experimentais, os coeficientes k e β presentes na expressão simplificada da NBR 9062 para o cálculo da rigidez secante. Os valores calculados para esses coeficientes podem servir de valores indicativos e orientativos para projetistas estruturais e para futuras pesquisas.

In this paper, an optimization process using MATLAB-SAP2000 Open Application Programming Interface (OAPI) is presented for optimum design of space frames with semi-rigid connections. A specified list including W-profiles taken from American Institute of Steel Construction (AISC) is used in the selection of suitable sections. The stress constraints as indicated in load and resistance factor design of AISC, lateral displacement constraints being the top- and inter-storey drift and geometric constraints are considered in the optimization process. Genetic algorithm method based on biological principles and harmony search algorithm method based on the processes of musical harmony are used for optimum designs. Two different space frames are solved for the cases of rigid and semi-rigid connections, separately. A computer program is coded in MATLAB for the purpose interacting with SAP2000 OAPI. Results obtained from the analyses show that type of semi-rigid connections plays a crucial role in the optimization of steel space frames and increases the optimum weight. © 2016, The Natural Computing Applications Forum.

Composite connections are defined as regions where composite beam frames into a steel column. A composite flange plate connection with web cleats is studied here since it is expected to give adequate seismic performance at minimum cost. A modification of the traditional flange plate connection, termed as stiffened flange plate connection is also suggested and its merits over the flange plate connection are assessed. Since in the flange plate and stiffened flange plate connections, the bolts are under shear and the problem of seat angle opening up under sagging moments is avoided, they are expected to perform equally well under sagging and hogging moments. To study the cyclic behaviour incremental amplitude cyclic tests were done on two interior joint sub-assemblages, one with a flange plate connection and the other with a stiffened flange plate connection as the means to transfer moment. The flange plate and stiffened flange plate connections showed adequate energy dissipation capacity and ductility to be used in seismically active regions. � 2013 Elsevier Ltd.

Choosing "an idealized model of the structure" in the classical theory of structures, connections between the members of the linear systems are usually adopted as ideally pinned or absolutely rigid. Ideally pinned connection does not allow relative displacement of interfaced sections foci, while sections can freely and independently rotate. The rigid connection does not allow both relative displacement and relative rotation. Numerous studies based on experimental results and numerical simulations, which were conducted over the last forty years, indicate that a large number of the node connections of members of linear systems can be classified neither as an ideally pinned nor as absolutely rigid. Systematization of recent results of scientific research, both theoretical and experimental work in this field in our country and worldwide, especially in the field of reinforced concrete linear systems, is performed in the first part of this doctoral thesis. The Chapter 1 presents an introductory discussion and an overview of the development of methods for analysis of linear girders, while in the Chapter 2 the results of the international project COST C1 ˝Semi- Rigid behavior˝ are analyzed in details, especially within the working groups for prestressed and reinforced concrete structures and seismic design. A special contribution to the study of this problem in our country is given by numerous theoretical and experimental works of the team of researchers from the Faculty of Civil Engineering in Niš under the leadership of Prof. Dr. Milic Milicevic. The theoretical approach to the design of structures with semi-rigid connections using the classical formulation of deformation method was analyzed in these works in details which an overview is given in the Chapter 3. Bearing in mind that the contemporary analysis of stress-strain state of complex engineering structures can not be imagined without a matrix formulation and implementation of electronic computers, the matrix formulation of structural analyzes of systems with semi-rigid connections is presented in the same chapter, which opens wide opportunities for relatively quick and simple analysis of these systems by use of modern methods of structural analysis. Variation formulation of the stiffness matrix and the equivalent load vector determination is shown in the Chapter 4, while the use of computers in the analysis of structures with semi-rigid connections is given in the Chapter 5. The results of the full size experimental analysis of a behavior of prefabricated reinforced concrete structures with semi-rigid connections carried out on the newly designed and constructed buildings Minoma and cold storage Lovopromet in Nis under static load are presented in the Chapter 6. In Chapter 7 is shown the experimental determination of the dynamic characteristics of structures by ambient vibration method which is performed on buildings constructed in structural systems Minoma and Amont in Nis. In the second part of the doctoral thesis experimental study is shown, which was realized in cooperation with the "Institute of Earthquake Engineering and Engineering Seismology" of the University St. Cyril and Methodius, Skopje, Republic of Macedonia, as a part of the static and dynamic stability attesting project of the standardized modulus of prefabricated RC halls program of structural system "AMONT", including analysis of obtained results, numerical modeling and calculation of reinforced concrete linear structures constructed in this system taking into account the real characteristics of connections. Almost all earthquakes that have occurred in the world in recent decades have caused severe damage or total demolition of precast reinforced concrete structures with semi-rigid connections (industrial iv halls and other various structures which differ in number of floors and ground floor typology). The most important is to provide that there are no human casualties during this damage, but the demolition of these buildings during the earthquake causes huge losses. In addition to the losses in terms of the economic value of the building itself, demolition most often has caused destruction of the very expensive industrial equipment. Modern technological lines in contemporary industry may be five to ten times more expensive than the value of the building itself. If the long-term economic consequences of the termination of the production process are taken into account, it is clear that the seismic safety of industrial halls is of vital importance in any seismically vulnerable region, which includes the territory of Serbia. In the second part of the doctoral thesis original results obtained on the basis of extensive theoretical and experimental research are presented with the aim to give adequate contribution in the field of real observation of present problems, in order to define the structural conditions and measures to improve the seismic safety of these specific structural systems. For this purpose primarily real phenomena and causes of damage and demolition of similar buildings during earthquake action are studied (Chapter 8). Based on the selected characteristic prototype of an industrial hall, which is widely present in Serbia, very extensive program of experimental research was carried out. These studies have provided original results and new insights into the real behavior of structural connections based on constructed full size physical models testing under the simulated cyclic load to the point of failure (Chapter 9). Improved methodological concept for nonlinear analysis of integral facilities with semi-rigid connections is formulated on the base of the experimental results by use of totally non-linear mathematical model (Chapter 10). A consistent theoretical procedure applicable for a detailed analysis of nonlinear seismic response of the systems with semi-rigid connections has been formulated and presented in the Chapter 11. The methodological concept of developed computer software used for detailed analysis of nonlinear seismic response of the selected prototypical building is presented in the shortest in the Chapter 12. The analytical part of the specific research includes the realization of extensive analysis of nonlinear seismic response of the selected characteristic prototypical industrial hall, with the aim to show the practical applicability of formulated analytical model and theoretical procedure for nonlinear analysis. The concept of formulated totally nonlinear mathematical model is shown in the Chapter 13, while in the Chapter 14 and the Chapter 15 the most significant results of the performed analysis of nonlinear seismic response of the building in transversal and longitudinal direction due to the effect of real registered earthquakes are presented. The fundamental facts that have been reached on the basis of completed complex analytical research are stated in the Chapter 16. Formulated and implemented detailed nonlinear analyzes enable improved design and wide practical application of standardized industrial halls and other facilities of this type in seismic zones of various intensity.Based on the results of completed integral theoretical, experimental and analytical studies, adequate conclusions and appropriate recommendations for further experimental and analytical research are summarized in the Chapter 17.

A genetic algorithm-based minimum weight design method is presented for steel frames containing composite beams, semi-rigid connections and column bases. Genetic Algorithms carry out optimum steel frames by selecting suitable profile sections from a specified list including 128 W sections taken from American Institute of Steel Construction (AISC). The displacement and stress constraints obeying AISC Allowable Stress Design (ASD) specification and geometric (size) constraints are incorporated in the optimization process. Optimum designs of three different plane frames with semi-rigid beam-to-column and column-to-base plate connections are carried out first without considering concrete slab effects on floor beams in finite element analyses. The same optimization procedures are then repeated for the case of frames with composite beams. A program is coded in MATLAB for all optimization procedures. Results obtained from the examples show the applicability and robustness of the method. Moreover, it is proved that consideration of the contribution of concrete on the behavior of the floor beams enables a lighter and more economical design for steel frames with semi-rigid connections and column bases. Copyright © 2015 Techno-Press, Ltd.

In this paper, an optimization process using Genetic Algorithm (GA) that mimics biological processes is presented for optimum design of planar frames with semi-rigid connections by selecting suitable standard sections from a specified list taken from American Institute of Steel Construction (AISC). The stress constraints as indicated in AISC-LRFD (American Institute of Steel Construction - Load and Resistance Factor Design), maximum lateral displacement constraints and geometric constraints are considered for optimum design. Two different planar frames with semi-rigid connections taken from the literature are carried out first without considering concrete slab effects in finite element analyses and the results are compared with the ones available in literature. The same optimization procedures are then repeated for full and semi rigid planar frames with composite (steel and concrete) beams. A program is developed in MATLAB for all optimization procedures. Results obtained from this study proved that consideration of the contribution of the concrete on the behavior of the floor beams provides lighter planar frames. © 2015 Techno-Press, Ltd.

Las matrices de rigidez y de carga de primer y segundo orden de una viga-columna de Timoshenko ortotrópica de sección transversal simétrica con conexiones semirrígidas incluyendo los efectos de la carga axial en los extremos (tracción o compresión) y de las fuerzas cortantes a lo largo del elemento fueron deducidas en el primer artículo. El modelo de Haringx descrito por Timoshenko y Gere (1961) fue adoptado en la formulación de las matrices. Ambas matrices serán utilizadas en los análisis elásticos de estabilidad, de primer y de segundo orden de estructuras aporticadas con elementos viga-columna de Timoshenko de sección transversal simétrica con conexiones rígidas, semirrígidas y simples en los cinco adjuntos en este artículo. Estudios analíticos indican que la carga de pandeo y la rigidez de estructuras aporticadas son reducidas por efecto de la deformación por cortante a lo largo de cada elemento. Además, el fenómeno de pandeo bajo fuerzas de tracción en elementos con rigidez a cortante relativamente baja es incluido en las ecuaciones propuestas. El pandeo por tracción no debe ser ignorado en el análisis de estabilidad de elementos viga-columna con rigidez a cortante GAs del mismo orden de magnitud que EI/h². La validez de ambas matrices es verificada con soluciones disponibles de análisis de estabilidad y de comportamiento elástico geométrico no lineal de estructuras viga-columna. Se incluyen cinco ejemplos que demuestran la eficiencia del método propuesto y de las matrices correspondientes. The first- and second-order stiffness and load matrices of an orthotropic Timoshenko beam-column of symmetric cross section with semirigid connections including the effects of end axial loads (tension or compression) and shear deformations along the member are derived in the first article. The “modified” stability approach based on Haringx´s model described by Timoshenko and Gere (1961) is utilized in all matrices. Both matrices are used in the stability, first- and the second-order elastic analyses of framed structures made of Timoshenko beam-columns with rigid, semirigid and simple connections of symmetric cross sections in the five examples included in this article. Analytical studies indicate that the buckling load and the stiffness of framed structures are reduced by the shear deformations along the members. In addition, the phenomenon of buckling under axial tension forces in members with relatively low shear stiffness is captured by the proposed equations. Tension buckling must not be ignored in the stability analysis of beam-columns with shear stiffness GAs of the same order of magnitude as EI/h². The validity of both matrices is verified against available solutions of stability analysis and nonlinear geometric elastic behavior of beam-column structures. Five examples are included that demonstrate the effectiveness of the proposed method and corresponding matrices.

Las matrices de rigidez y de carga de primer y segundo orden de una viga-columna de Timoshenko ortotrópica de sección transversal simétrica con conexiones semirrígidas incluyendo los efectos de la carga axial en los extremos (tracción o compresión) y de las fuerzas cortantes a lo largo del elemento son deducidas de una manera clásica. El modelo de Haringx descrito por Timoshenko y Gere (1961) es adoptado en la formulación de las matrices. Ambas matrices pueden ser utilizadas en los análisis elásticos de estabilidad, de primer y de segundo orden de estructuras aporticadas con elementos viga-columna de Timoshenko de sección transversal simétrica con conexiones rígidas, semirrígidas y simples. Las matrices de rigidez propuestas pueden también ser usadas en el análisis inelástico de pórticos cuyos elementos sufren de degradación por flexión o, en caso contrario, rigidización de las conexiones. Las expresiones cerradas de las matrices de rigidez y de carga desarrolladas y presentadas en este artículo encuentran grandes aplicaciones en los análisis de estabilidad y de segundo orden de estructuras aporticadas compuestas de elementos viga-columna con rigidez a cortante relativamente baja tales como polímeros compuestos ortotrópicos (FRP o “composites”) y elementos cortos elastoméricos de múltiples capas comúnmente usados como aislamiento sísmico en edificios. Los efectos del alabeo torsional a lo largo del elemento no son incluidos. The first- and second-order stiffness and load matrices of an orthotropic Timoshenko beam-column of symmetric cross section with semirigid connections including the effects of end axial loads (tension or compression) and shear deformations along the member are derived in a classical manner. Both matrices can be used in the stability, first- and the second-order elastic analyses of framed structures made of Timoshenko beam-columns with rigid, semirigid and simple connections of symmetric cross sections. The “modified” stability approach based on Haringx´s model described by Timoshenko and Gere (1961) is utilized in all matrices. The proposed stiffness matrices can also be used in the inelastic analysis of frames whose members suffer from flexural degradation or, on the contrary, stiffening at their end connections. The closed-form second-order stiffness matrix and load vector derived and presented in this paper find great applications in the stability and second-order analyses of framed structures made of beam-columns with relatively low shear stiffness such as orthotropic composite polymers (FRP or composites) and multilayer elastomeric bearings commonly used in seismic isolation of buildings. The effects of torsional warping along the members are not included. Analytical studies indicate that the buckling load and the stiffness of framed structures are reduced by the shear deformations along the members. In addition, the phenomenon of buckling under axial tension forces in members with relatively low shear stiffness is captured by the proposed equations. Tension buckling must not be ignored in the stability analysis of beam-columns with shear stiffness GAs of the same order of magnitude as EI/h². The validity of both matrices is verified against available solutions of stability analysis and nonlinear geometric elastic behavior of beam-column structures. Five examples are included that demonstrate the effectiveness of the proposed method and corresponding matrices.

Un nuevo conjunto de ecuaciones pendiente-deflexión para la viga-columna de Timoshenko de sección transversal simétrica con conexiones semirrígidas que incluyen los efectos combinados de deformaciones por cortante y por flexión, y los efectos de segundo orden causados por cargas axiales es desarrollado de una manera clásica. El método propuesto que también incluye los efectos de la componente de cortante de las fuerzas axiales aplicadas (modelo de Haringx) tiene las siguientes ventajas: 1) puede ser utilizado en la estabilidad y en el análisis de segundo orden de estructuras aporticadas compuestas de vigas y columnas de Timoshenko con conexiones rígidas, semirrígidas y simples; 2) los efectos de las conexiones están condensados dentro de las ecuaciones pendiente-deflexión para cargas axiales de tracción y compresión sin introducir grados de libertad ni ecuaciones adicionales; 3) es más exacto que cualquier otro método disponible en la literatura técnica y con la capacidad de capturar el fenómeno del pandeo de columnas bajo fuerzas de tracción axial; 4) es poderoso, práctico, versátil y fácil de enseñar. Estudios analíticos indican que las deformaciones por cortante incrementan las deflexiones laterales y reducen la cargas críticas axiales de estructuras aporticadas hechas de columnas y vigas con baja rigidez a cortante. A new set of slope-deflection equations for Timoshenko beam-columns of symmetrical cross section with semi-rigid connections that include the combined effects of shear and bending deformations, and second-order axial load effects is developed in a classical manner. The proposed method that also includes the effects the shear component of the applied axial forces (Haringx Model) has the following advantages: 1) it can be utilized in the stability and second-order analysis of framed structures made up of Timoshenko beam-columns with rigid, semi-rigid, and simple end connections; 2) the effects of semi-rigid connections are condensed into the slope-deflection equations for tension or compression axial loads without introducing additional degrees of freedom and equations; 3) it is more accurate than any other method available and capable of capturing the phenomena of buckling under axial tension forces; and 3) it is powerful, practical, versatile and easy to teach. Analytical studies indicate that shear deformations increase the lateral deflections and reduce the critical axial loads of framed structures made of members with low shear stiffness.

The study of the stiffness of laterally loaded semi-rigid connections in plywood-timber beams is justified by the influence that the deformation of the connection has on the overall displacements of the structure. Semi-rigid connections are characterized by the occurrence of a slip between the connected pieces. The characterization of a connection is usually based on an isolated single connector behavior, which is described by its load-slip relationship expressed by the slip modulus, and so it is extended to the group of connectors. Although the method of analysis is well established, the concept of equivalent slip modulus, defined as the slip modulus per unit length of a connection, has not been totally explored. In this study, we focus on the experimental determination of the equivalent slip modulus for mechanically analyzing plywood-timber beams with continuous connections. The results demonstrated that the test is suitable for obtaining experimental values of the equivalent slip modulus.