Eksperimentalne in numerične preiskave za določitev kontroliranega odziva večslojne kamnite zidovine

V sklopu naloge je bilo študirano obnašanje troslojnih kamnitih zidov, in sicer obnašanje pri tlačnih obremenitvah in pri strižnih obremenitvah v ravnini zidov. Izvedene so bile obsežne eksperimentalne preiskavetlačni in strižni testi skupaj 18 zidov ter spremljajoče preiskave konstituentov (malte in kamna). Preskušani kamniti zidovi so značilni predvsem za reprezentativne starejše objekte, ki pogosto predstavljajo pomemben del naše kulturne dediščine. Za testiran tip zidov je bil sistematično analiziran vpliv morfologije zidov (sestave po prerezu), različnih nivojev pred-obremenitev ter robnih pogojev vpetja na različne karakteristike obnašanja zidov. Poleg nosilnosti je bil poudarek na analizi pomikov ter poškodovanosti zidov v karakterističnih stanjih obnašanja. V odvisnosti od robnih pogojev je pri strižnih testih prišlo do različnih porušnih mehanizmov zidovupogibnega, mešanega in diagonalnega strižnega, pri čemer v nasprotju s pričakovanji izven-ravninski mehanizem ni bil merodajen. Do slednjega je prišlo bolj opazno pri višjih pred-obremenitvah zidov v fazi mehčanja zidov. Za testirani tip zidov povezovalni kamni preko prereza zidu niso prispevali ne k večji nosilnosti ne k večjim mejnim pomikom. Eksperimentalni rezultati nosilnosti in mejnih zasukov so bili primerjani z analitičnimi modeli. Strižno nosilnost se zadovoljivo oceni z obstoječimi modeli za porušitve, do katerih je pri testih dejansko prišlo. Doseženi mejni pomiki zidov so bili pri testih veliko večji, kot so dovoljeni mejni pomiki v standardih (EN 1998-3 in FEMA 306). Ker je pri objektih kulturne dediščine poleg same konstrukcije pogosto v interesu ščititi tudi različne poslikave, je bil na zidove nanesen apneni omet, ki je služil študiju obnašanja umetnostih elementov zidov. Določene so bile vrednosti mejnih zasukov zidov za 4 stanja poškodb ometov, ki so uporabne za oceno potresne odpornosti objektov s stališča poškodovanosti ometov. Drugi del naloge obravnava utrjevanje poškodovanih troslojnih kamnitih zidov. Ker je navadno pri utrjevanju historične zidove zahtevana uporaba kompatibilnih materialov, reverzibilnost ukrepov, itd., je bil v sklopu naloge razvit nov sistem utrjevanja. Poškodovani zidovi so bili injektirani s cementno-apneno injekcijsko mešanico in dodatno utrjeni s stekleno vrvico, s podaljšano apneno malto vgrajeno v horizontalne maltne spojnice, ter z vrvico tudi prečno povezani. Skupaj je bilo z različnimi kombinacijami ukrepov utrjenih in dodatno testiranih 10 zidov. Injektiranje se je izkazalo kot primeren sanacijski ukrep, vrvice v spojnicah pa so povečale duktilnost zidov ter v določenem primeru tudi nosilnost. Rezultati testov neutrjenih zidov so bili aplicirani na dejanski objekt. Na primeru Vile Vipolže je bil numerično analiziran vpliv predpostavke mejnih pomikov zidov na potresno obnašanje objekta, računano z nelinearno statično analizo konstrukcije na modelu z ekvivalentnimi okvirji. Glede na rezultate (nezanemarljivo povečanje odpornosti v primeru povečanja pomikov) bi bilo za bolj duktilno zidovino, kot je navadno zgodovinska, smiselno dodatno preučiti smotrnost povečanja mejnih vrednosti zasukov v predpisih.In the thesis, the behaviour of three-leaf stone masonry walls under compression loading and in-plane shear loading is studied. An extensive experimental campaign was conducted on 18 walls, accompanied by tests on masonry constituents (mortar and stone). The type of the tested masonry is typical for older representative buildings, which often present important cultural heritage assets. Influence of morphology, level of pre-compression and boundary conditions on various characteristics of the walls behaviour was systematically studied. Besides the strength, the greatest emphasis was on the analysis of the displacement capacity and damage of the walls at characteristic stages of their response. Due to various boundary conditions, different failure mechanisms developedrocking, mixed and diagonal shear. Leaf separation and the out-of-plane mechanism of the wall was not critical as expected. It developed more evidently in the post-peak phase of the tests for specimens with higher pre-compression. The presence of connecting stones had no influence neither on the obtained shear strength nor on the displacement capacity of the walls. The experimental results were compared to results of analytical models for prediction of shear resistance. For the tested type of masonry, shear strength can be adequately estimated with existing models for the failure mechanisms that developed in the tests. Drift capacity of the walls was however significantly higher than drift capacity allowed in the code provisions (EN 1998-3 in FEMA 306). In heritage buildings also various artistic assets in the form of painted walls are often present. Lime plaster was applied to the walls in order to study its performance during cyclic shear loading. Reference drift values for walls at 4 different characteristic plaster damage states were determined. They can be used for performance based seismic assessment of historic buildings. The second part of the thesis deals with strengthening of the damaged three-leaf stone masonry walls. For monumental buildings there are usually strict demands upon the use of materials compatible to existing materials, reversibility, etc., therefore a new strengthening system was developed. Walls were retrofitted along the cracks with lime-cement grout, additionally strengthened with near surface mounted (NSM) glass cords and transversally connected10 walls were strengthened with various combinations of measures and re-tested. Grouting successfully retrofitted the walls, while NSM glass cords increased the displacement capacity and, in one case, also shear resistance substantially. Finally, the results of tests of the un-strengthened walls (drifts) were adopted for the numerical analysis of the seismic performance of an actual building (mansion Vipolže). Nonlinear static analyses using equivalent frame model were conducted. The influence of the assumed drift limits on the seismic resistance was analysed. The increase of seismic performance with increasing drift limits of walls is evident and it would be reasonable to further study the prospect of increasing the drift limits in the code provisions for types of masonry, which are more ductile (historical masonry)

Vulnerability Study of Urban and Rural Heritage Masonry in Slovenia Through The Assessment of Local and Global Seismic Response of Buildings

Uncertainties regarding the influence of modelling strategies for the evaluation of seismic vulnerability of\ud masonry buildings in Slovenia were studied on two case studies– damaged buildings from the rural area of NW\ud Slovenia hit by earthquakes in ’98 and ’04 and the urban buildings from the old city centre of Ljubljana. Two\ud strategies were applied – failure mechanisms analysis by means of FaMIVE methodology and non-linear\ud response analysis by means of storey and global response (SREMB and 3Muri). The accuracy in predicting\ud failure modes by FaMIVE was 50% considering the stock of investigated building in rural area. The most critical\ud failure mechanisms were due to out-of-plane loading. For urban architecture, in-plane failure due to weak\ud spandrels was the predominant one. The mechanism assessment yields more conservative results in respect to\ud non-linear approach and thus may be an efficient tool for the design of strengthening measures for heritage\ud buildings to prevent damage in lower intensity events with higher probability of occurrence

Influence of Ageing and Deterioration of Masonry on Load Bearing Capacity of Historical Building

Numerous heritage buildings in the former Eastern Europe that were neglected in the past are severely deteriorated due to ageing and moisture problems. The paper summarizes experimental and numerical work carried out on 150 yrs. old Kolizej Palace in Ljubljana (Slovenia) which has recently been demolished, despite the overall opinion among conservators that it should be preserved. Experimental tests proved almost completely saturated conditions in the ground level of the building, while all the stories above were in almost dry condition. The results of tests on masonry revealed that moisture content and state of deterioration affected both strength and stiffness properties of built masonry in that extend so that the previous estimations and calculations regarding the state of the structure and its static load bearing capacity were too optimistic. Both storey and global response non-linear seismic analysis have proved that building in its current condition is far below the current seismic code requirements

Cyclic response of insulated steel angle brackets used for cross-laminated timber connections

In cross-laminated timber (CLT) buildings, in order to reduce the disturbing transmission of sound over the flanking parts, special insulation layers are used between the CLT walls and slabs, together with insulated angle-bracket connections. How-ever, the influence of such CLT connections and insulation layers on the seismic resistance of CLT structures has not yet been studied. In this paper, experimental investigation on CLT panels installed on insulation bedding and fastened to the CLT floor using an innovative, insulated, steel angle bracket, are presented. The novelty of the investigated angle-bracket connection is, in addition to the sound insulation, its resistance to both shear as well as uplift forces as it is intended to be used instead of traditional angle brackets and hold-down connections to simplify the construction. Therefore, monotonic and cyclic tests on the CLT wall-to-floor connections were performed in shear and tensile/compressive load direction. Specimens with and without insulation under the angle bracket and between the CLT panels were studied and compared. Tests of insulated specimens have proved that the insulation has a marginal influence on the load-bearing capacityhowever, it significantly influences the stiffness characteristics. In general, the experiments have shown that the connection could also be used for seismic resistant CLT structures, although some minor improvements should be made

In-plane seismic behaviour of ashlar three-leaf stone masonry walls

In light of the forthcoming second generation Eurocodes (EC), the results of conducted systematic in-plane cyclic and compressive tests on three-leaf stone masonry walls are discussed following new requirements and provisions. The new proposal for EC8-3 for existing buildings is based on partial factors safety approach, though it considers different uncertainties in defining input parameters for effective seismic performance-based assessment. Prior to its application, massive calibration effort will be needed since there is no standardized method for shear testing of masonry walls. In this paper, the performance limit states damage, resistance, and displacement capacities from conducted test results were evaluated and assessed through comparison with analytical solutions and imposed limit values, as stated in existing codes. The test results provide a much higher deformation capacity than the limits provided in both existing and new proposal of EC8-3 as well as those in the ASCE code provisions. The reason for this lies in the soft, "ductile" mortar for which the presumed resistance according to code provisions should be significantly higher when considering good quality ashlar three-leaf stone masonry

Composite beams made of waste wood-particle boards, fastened to solid timber frame by dowel-type fasteners

To increase the sustainability of prefabricated timber buildings and constructions, composite timber beams with “box” cross-sections were developed in collaboration with an industry partner. They were constructed from a solid timber frame and from webs made of residual waste wood- particle boards from prefabricated timber buildings production. The developed beams’ design concepts presented in this paper were governed by architectural features of prefabricated timber buildings, geometrical limitations, available production technology, and structural demand related to various possible applications. The paper presents the results of experimental bending tests of six variations of the developed composite timber beams constructed by mechanical fasteners only. The developed design concept of composite timber beams without adhesives is beneficial compared to glued beams in terms of design for deconstruction and lower VOC emissions. The tests were conducted to study the influence of the following parameters on the beams’ mechanical behavior: (i) web material (oriented strand boards (OSBs) vs. cement-particle boards)(ii) the influence of beam timber frame design (flanges and web stiffeners vs. flanges, web stiffeners, and compressive diagonals), and (iii) the influence of stiffener–flange joint design. Besides the beams’ load-bearing capacities, their linear and non-linear stiffness characteristics were the main research interest. While adding compressive timber diagonals did not prove to significantly increase the stiffness of the beams in the case of cement-particle board webs, it increased their load-bearing capacity by enabling the failure of flanges instead of prior webs and stiffener–flange joints failure. For beams with OSB webs, failure of the bottom flange was achieved already with the “basic” timber frame design, but timber diagonals proved beneficial to increase the stiffness characteristics. Finally, mechanical characteristics of the developed beams needed in structural design for their application are provided together with further development guidelines

Improved seismic response of light-frame-timber panels with cement-particle-board sheathing of various thicknesses and different configurations of fasteners

Due to their comparable fire characteristics and surface preparation, light-frame timber panels using cement-particle boards (CPB) as a sheathing material present a potential alternative to gypsum-fibre boards. An experimental campaign was conducted to evaluate the behaviour of CPB light-frame-timber panels under in-plane lateral loading. Monotonic and cyclic in-plane shear tests were conducted on full-size panels, following preceding tests on the stapled sheathing-to-timber connections used in the panels. The influence of the boards’ thickness and staple geometry on the response of connections and panels was studied, also on panels with an asymmetrical CPB layout, which proved not to have a negative influence on the panels’ lateral load-bearing capacity. Furthermore, in order to improve the seismic response, panels, which had almost twice the number of staples compared to the basic panel, were testedone variation with two rows of staples, and the other with the staples spaced closer together, such that the spacing distance was halved. The tests revealed a significant, though not proportional, increase in lateral resistance in the strengthened panels. Fastening the CPB with two rows of staples proved the better option, since subsequent failure of the CPB along the connections, as opposed to ductile failure of the staples in the basic panels, proved not to reduce the panels’ deformation capacity. The paper also compares the test results of the connections and panels to analytical results according to Eurocode 5 (EC5), the European code provision for the design of timber structures

The influence of flexible sound insulation layers on the seismic performance of cross laminated timber walls

This paper presents the results of an experimental campaign investigating the seismic behaviour of full-size cross laminated timber (CLT) wall systems with sound-insulated shear-tension angle brackets. The main aim of the study was to investigate the influence of more and less flexible soundproofing bedding under the CLT wall. The paper shows a comparison of lateral load-bearing capacity, displacement capacity, ductility and stiffness obtained from racking tests on uninsulated specimens and specimens with various types of bedding insulation and levels of vertical load. Moreover, an analytical procedure to estimate the lateral load-displacement response of CLT walls with bedding insulation is proposed. This model is verified by direct comparison to the experimentally determined lateral load-displacement backbone curves. The results show that the elastomeric bedding does not have a significant effect on the bearing capacity of the wall system tested, but it reduces the stiffness and increases the displacement capacity. Due to the large decrease in stiffness, the insulation causes an overall reduction in ductility. The analytical estimation proposed was able to capture the reduction in lateral stiffness and adequately predict the load-bearing capacity

Vulnerability Study of Urban and Rural Heritage Masonry in Slovenia Through The Assessment of Local and Global Seismic Response of Buildings

Uncertainties regarding the influence of modelling strategies for the evaluation of seismic vulnerability of masonry buildings in Slovenia were studied on two case studies- damaged buildings from the rural area of NW Slovenia hit by earthquakes in ʼ98 and ʼ04 and the urban buildings from the old city centre of Ljubljana. Two strategies were applied - failure mechanismsanalysis by means of FaMIVE methodology and non-linear response analysis by means of storey and global response (SREMB and 3Muri). The accuracy in predicting failure modes by FaMIVE was 50% considering the stock of investigated building in rural area. The most critical failure mechanisms were due to out-of-plane loading. For urban architecture, in-plane failure dueto weak spandrels was the predominant one. The mechanism assessment yields more conservative results in respect to non-linear approach and thus may be anefficient tool for the design of strengthening measures for heritage buildings to prevent damage in lower intensity events with higher probability of occurrence