Teorijska i eksperimentalna analiza armiranobetonskih linijskih nosača sa polukrutim vezama

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

Static Design of Systems with Semi-Rigid Connections Based on Experimental Investigation of the Full Scale Structure

The paper presents the basic theory and corresponding equations for calculation of the static influences of the structures with semi-rigid connections in joints. The static design of system in which connections of members are absolutely rigid or perfectly pinned has been thoroughly worked out in the existing literature. In real structures in general, and particularly in the precast ones, connection in joints may be partially rigid, which can have a significant impact on the change of stresses and strains in the structure. In the world there are several procedures, with different approaches, to the structural design with semi-rigid connections, however, it is proved that they all lead to the same results. All of these approaches in addition to theoretical deal with experimental analysis of results. According to the approach that will be presented in this paper, typical prefabricated structures "Minoma" 1, "Minoma" 2, and "Minoma" 3 with span of 12m, 20m and 27m respectively, and the height of the column up to 9m, have been experimentally analyzed. A numerical example will be given and discussed, where bending moments due to a given load, as well as due to input force in the tensioner, have been calculated for defined levels of rigidity of connection using the deformation method. The obtained superimposed bending moment diagram will be analyzed too

Analysis of a potential collision of buildings during earthquake based on computer simulation

U slučajevima kada dilatacijske razdjelnice između susjednih zgrada nisu dovoljne, za vrijeme zemljotresa sudaraju se pojedini dijelovi objekata. Pri tome dolazi do lokalnih oštećenja ili čak rušenja dijelova zgrada jer su sile udara velikog intenziteta. Da bi se to izbjeglo, treba posebnu pažnju posvetiti projektiranju aseizmičkih razdjelnica. U radu je prikazana parametarska analiza potencijalnog sudara dvije višespratne zgrade, primjenom programskog paketa SAP2000v15, s ciljem da se ispita što se dešava ako su razdjelnice projektirane u skladu sa standardima koji važe u Srbiji, a ipak dođe do sudara u nekim razmatranim slučajevima. Korišten je model s fleksibilnom osnovom u interakciji s tlom. U dinamičkoj su analizi korišteni akcelerogrami realnih zemljotresa. Određene su vrijednosti seizmičkih sila, momenata savijanja i normalnih sila u slučajevima kada bi došlo do sudara zgrada, kao i potrebna širina dilatacijskih razdjelnica da bi se izbjegao sudar, a izvedeni su i zaključci o utjecaju pojedinih parametara na pojavu sudara.In the cases when expansion joints between adjacent buildings are not sufficient, certain parts of the structure collide during earthquake. Then it comes to local damage or even destruction of parts of the building because of the impact forces of great intensity. In order to avoid collision, particular attention has to be paid to design of aseismic joints. In the paper, a parametric analysis of the potential collision of two multi-storey buildings is carried out by the use of software package SAP2000v15, with the goal to examine what occurs if the expansion joints have been designed in compliance with Serbian standards, and if yet there are collisions in some cases. The flexible base model in interaction with soil was designed. The accelerograms of real earthquakes were applied in dynamic analysis. Quantities of seismic forces, bending moments and axial forces in the case of collision, as well as necessary width of expansion joints to avoid it, were computed. Conclusions about influence of considered parameters on collision occurrence were accomplished

Teorijska i eksperimentalna analiza armiranobetonskih linijskih nosača sa polukrutim vezama

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

SEIZMIČKA ANALIZA RAMOVA SA POLUKRUTIM VEZAMA U SKLADU SA EC8

Up to date research has pointed out that most of the structural connections of reinforced concrete (RC) frames, particularly precast ones, behave as semi-rigid. Therefore, it is of great importance to develop an analysis method which takes into account the connection rigidity. For that purpose matrix formulation of the deformation method is used in this paper, and the effect of rigidity of connections on the structure response is included by stiffness matrix for semi-rigidly connected member. The elements of this matrix are functions of the fixity factors at the ends of members. The proposed method is applied in seismic analysis of the precast RC frame structure of the existing industrial hall according to Eurocode 8 (EC8).Dosadašnja istraživanja su pokazala da se većina konstruktivnih veza armiranobetonskih (AB) ramova, posebno montažnih, ponaša kao delimično krute. Zbog toga je od velike važnosti razviti metod analize koji uzima u obzir krutost veze. U ovom radu je za to korišćena matrična formulacija metode deformacije, a uticaj krutosti veza na odziv konstrukcije obuhvaćen je matricom krutosti za delimično kruto vezani štap. Elementi ove matrice su funkcije stepena uklještenja na krajevima štapova. Predložena metoda je primenjena u seizmičkoj analizi prefabrikovane AB ramovske konstrukcije postojeće industrijske hale u skladu sa Evrokodom 8 (EC8)

Semi-Analytical Solution for Elastoplastic Deflection of Non-Prismatic Cantilever Beams with Circular Cross-Section

A solution for the elastoplastic deflection of cantilever beams with linearly variable circular cross-section loaded by shear force at the free end, which is suitable for practical use, has not yet been developed. A semi-analytical solution for such a problem is proposed in this paper. The solution involves beams made of homogenous and isotropic materials with bilinear elastoplastic strain hardening behavior. The Bernoulli–Euler formula is used for determining the elastic deflection. However, for the plastic domain of material behavior, the differential equation of beam bending does not have a solution in closed form. Therefore, an incremental procedure for determining the curvature of the plastified region of the beam is suggested. Deflection of the cantilever beam is calculated via integration of the approximated function of the beam curvature. The proposed semi-analytical solution is validated using experimental results of the seismic energy dissipation device components which have been selected as a sample of a real engineering system. Also, validation is done via finite element analysis of six different cantilever beam models with varying geometric and material characteristics. A satisfying agreement between the proposed semi-analytical results and the subsequent experimental and numerical results is herein achieved, confirming its reliability

REDISTRIBUTION OF THE INFLUENCES IN SYSTEMS WITH SEMI-RIGID JOINTS ON ELASTIC FOUNDATIONS

Abstract. Most often, in the case of typefied prefabricated systems, foundations are designed and constructed as prefabricated elements as well. When the structure is exposed to high intensity loading and founded on a weak soil, beam foundations are often used instead of pad foundations. Beam foundations, stiffening girders, as well as beams which support the façade elements or partition walls, are treated as beams on elastic foundations, while joint of these girders to pad foundations or vertical support elements of a precast structure can be treated as semi-rigid. Modeling of systems with semi-rigid joints on elastic foundations, for different levels of rigidity of connections, is illustrated by an example of a frame under static loading. On the basis of the results of the calculation carried out in this paper, it is evident that taking into account the elastic foundations of the member and the corresponding degree of fixation of the member on this foundations significantly affects the magnitude of the forces in the cross-sections of the member, and on the redistribution of influences in the entire structure. Yet, the foundations-and-soil interaction exerted the highest influence on the magnitude of the stress in the foundation structure itself. Key words: precast structure, semi-rigid connection, redistribution of influences. 1

ANALITIČKA PREDIKCIJA MEHANIČKIH KARAKTERISTIKA U HORIZONTALNOM PRAVCU GUMENOG LEŽIŠTA SA OLOVNIM JEZGROM

Application of seismic isolation devices is an efficient way for designing seismically resistant structures. For that purpose, various types of seismic isolation devices are developed. The main differences between them are in the materials used for their production and in the way they provide horizontal flexibility. Dynamic analysis of a base isolated structure requires an adequate mathematical model of the seismic isolation devices which can describe their mechanical properties in horizontal and vertical directions. The paper is considering analytical models used for the prediction of mechanical properties in the horizontal direction of lead-rubber bearings, which are proposed in the contemporary literature. Results obtained using these analytical formulas are compared with the results obtained by the finite element analysis model developed in this paper, as well as with available test results provided by the manufacturer. Improvements of the existing analytical models are suggested in order to enable a better prediction of mechanical characteristics in the horizontal direction of lead-rubber bearings.Primena uređaja za seizmičku izolaciju je efikasan način za projektovanje seizmički otpornih konstrukcija. Razvijene su različite vrste uređaja za seizmičku izolaciju. Glavne razlike između njih se ogledaju u primenjenim materijalima i načinu na koji obezbeđuju horizontalnu fleksibilnost. Dinamička analiza bazno izolovanih konstrukcija zahteva adekvatan matematički model za opisivanje mehaničkih karakteristika u horizontalnom i vertikalnom pravcu uređaja za seizmičku izolaciju. U radu su analizirani analitički izrazi za predviđanje mehaničkih karakteristika u horizontalnom pravcu gumenog ležišta sa olovnim jezgrom. Rezultati dobijeni analitičkim izrazima su upoređeni sa rezultatima dobijenim na osnovu numeričkog modela metodom konačnih elemenata razvijenog u ovom radu i dostupnim rezultatima ispitivanja proizvođača. Postojeći analitički izrazi su unapređeni kako bi se adekvatnije definisale mehaničke karakteristike u horizontalnom pravcu gumenih ležajeva sa olovnim jezgrom

A BEARING STRUCTURE AND FINISHED CONSTRUCTION BEHAVIOR ANALYSIS BASED ON THE FULL-SCALE

Abstract. The paper deals with a brief presentation of a part of the performed experimental tests of the prefabricated reinforced concrete structural system "AMONT"for construction of various types of modern industrial halls. The test results are analyzed for two industrial halls both constructed according to this structural system but in the different phases of construction, tested in the full scale by application of AMBIENT vibration method. From the obtained Fourier spectra for measured ambient vibrations in two orthogonal direction for the structure without walls and the other with façade and filling walls, a significant discrepancy in their natural frequencies has been observed, and some conclusions about the influence of panel walls on dynamic characteristic the frame structure have been drawn out. The paper used some data of the research after the earthquake in Montenegro which took place on 15 th of April 1979