Restoring historic buildings is a challenging task in an environment where any insensitive or unprofessional intervention can cause irreparable damage. Among the most important demands currently placed on the construction industry are the protection of structural details, materials and technologies, and the extension of the life of these historic buildings. In this context, we should mention the protection of the high number of tenement buildings in European cities from the second half of the 19th and early 20th centuries, whose structural quality is relatively high and where many other building details and elements have been preserved. The brick dwellings of the period, which are between 85 and 170 years old, do not fully comply with many of the requirements and provisions of the current regulations and standards. The serious shortcomings of brick tenement buildings include, among other things, the inadequate thermal resistance of the envelope and infill structures and the high energy consumption of the operation of these buildings. This paper focuses on analysing this situation and defining the requirements for renovation, while preserving the architectural and historical values of urban buildings; achieving acceptable compliance with the requirements and provisions of the currently applicable regulations and standards; and demonstrating cost-effectiveness.

Historical masonry structures with a greater thickness can often be made as so called multi-leaf masonry with outer leaves lined with the application of some of the masonry bonding methods and with the inner leave of the so-called cast core formed by fragments of stones of different sizes that are bonded with more mortar. The load capacity, stiffness and the failure mechanism of multi-leaf masonry are influenced by the interaction of individual leaves with different deformation and physico-mechanical properties and the nature of the mutual connection of individual leaves of masonry. The performed analyses showed a significant influence of especially the cast core masonry tensile strength and the contact joint strength between the core masonry and the outer leaves.

AbstractThis article presents a proposal of a method for the restoration and rehabilitation of Liben Bridge, a historic concrete vaulted arch bridge structure from the early 20th century. The bridg...

The article briefly recalls the issue of historical buildings located in seismically active areas. In the introduction of the paper, the issue of the change of the dynamic response of the structure as a method for determining the possible damage of the structure, which can be difficult to detect by other diagnostic procedures, is discussed. Furthermore, the article outlines the procedure for determining some significant characteristics (such as bending stiffness etc.) by means of the dynamic response of the structure, and simplified relationships and recommendations for diagnosing arch structures based on its dynamic response. The focus of the paper is on the general analysis of the results of experimental tests of five segmental barrel vaults, of which two were reinforced with CFRP strips subjected to alternating static and dynamic loads. Due to the structure of the vault - single-layer masonry with a thickness of 150 mm - a loading mode was required. In the article conclusion the test results are interpreted with regard to the above mentioned facts (extent of experimental loading, specific vault structure) and it is stated that they have demonstrated the possibility of using a change of dynamic characteristics as a possible diagnostic method of the origin and development of defects on the vault structure

The grouting of historic masonry with degraded binders or masonry units, masonry with insufficient load-bearing capacity, masonry damaged by cracks, with a high void content and cavities and multi-leaf masonry is one of the rehabilitation methods of masonry frequently applied in practice, restoring its integrity and increasing its load-bearing capacity.

One of the frequently used methods of stabilization and reinforcement of historic masonry is grouting, especially grouting of cracks and voids in masonry structures. Determination of the properties of the injected structure, both in terms of physico-mechanical properties (with regard to the subsequent compatibility of the grouting mixture) and in terms of its condition and failures (cracks, voids, cavities), is a prerequisite for correct design and realization of reinforcement grouting. Minimization of interventions into the historic structure while performing surveys and the associated use of non-destructive diagnostic methods is one of the requirements for the remediation of listed buildings. Within the experimental research of reinforcement of historic masonry structures, the possibility of using thermography and ultrasound methods was evaluated and conditions and limitations for the use of these non-destructive methods were formulated.

The article presents partial results of experimental and theoretical research into the response of segmental masonry barrel vaults laid on wall support segments with different tie rod stiffness to alternating static and dynamic loading. The vaults were reinforced with non-prestressed carbon composite strips of high-strength fibres and epoxy resin (CFRP) alternatively arranged on the extrados or intrados of the vaults. The experimental results, in line with the assumption, demonstrated a moderate decrease in stiffness of the vault after each loading cycle of static and dynamic loads. The vault reinforcement proved to significantly increase the resistance of the vault to repeated static and dynamic loads

The article will present the principal results of theoretical analysis of controlling the dynamic characteristics of a multi-storey frame structure composed of precast columns and cross beams, which are mutually interconnected by demountable dry joints and thin-walled diaphragms. The embedded thin-walled precast reinforced concrete diaphragms are connected with the frame structure via discrete connections. The discrete connections are designed using the principle of contact rubber (elastomeric) bearings whose number, distribution and stiffness (particularly shear stiffness) are specified based on the magnitude and intensity of static and dynamic effects. The elastomeric bearings, their dynamic characteristics, number and distribution are the essential factors affecting the nature and intensity of the system's response to static and dynamic effects. The theoretical analysis based on experimentally identified characteristics of elastomeric bearings and a frame structure segment with an embedded diaphragm with elastomeric bearings has manifested a potential for reaching the required dynamic properties of the structure, damping and response of the structure to dynamic effects. The issues related to the response and resistance of building structures to the effects of dynamic loading are currently a focus of great interest worldwide. The presented design of a structure with controlled response represents an actual solution to the issue of securing the safety of structures in seismic regions.

The article presents the main results of experimental and theoretical research into the effect of grouting on the physical and mechanical properties of historic masonry. The subject of research are masonry structures of brickwork, natural stone (sandy marlstone, sandstone, limestone, trachyte) and mixed masonry with different degrees of binder degradation and polymer- and mineral-based grouting agents. The effect of grouting is verified through analyses including strength, modulus of elasticity and some other physical characteristics (porosity, absorption capacity). The research is carried out on segments of masonry structures with dimensions of 300x450x420mm (brick masonry), 550x650x750mm (stone and mixed masonry). Individual sets of test pieces differ by the degree of binder degradation. Depending on the characteristics of the grouting agent the grouting is performed either as low-pressure or jet grouting. The current research is also aimed at verifying special grouting mixtures developed at the researcher's workplace, based on mineral substances with nanoparticles.

The article will present the main results of experimental and theoretical research into non-reinforced barrel vault constructions and barrel vault construction reinforced with composites based on high-strength fibres and epoxy resin, or special polymer cement mortar. Vaulted constructions of historic and heritage buildings are extremely sensitive to deformations of the supporting construction, and their response to seismic effects may often be accompanied by cracking and mechanical vault failures. The results of research and study into the dynamic behaviour of barrel vaults brings new knowledge applicable in the prevention of vault failures in regions with an increased intensity of natural or technical seismicity, for the identification and localisation of failures using e.g. MAC or COMAC criteria. It can also be valuable in their serviceability assessment and service life extension. The second part of the article presents the results of theoretical and experimental analysis and a practical example of the stabilisation and reinforcement of 16 extensively damaged barrel vaults (with a 3.05 m span) with large lunettes situated over the cloister in the Premonstrate Monastery in Teplá (built in the 16th century), located in a seismically active region of West Bohemia.

The issues of the response of buildings to dynamic loading effects caused by natural seismicity have become a focus of great interest worldwide. According to the latest observations and calculations, the seismic hazard for buildings, mainly in seismically active regions of the Czech Republic, has increased, together with the area of the territories where buildings must be assessed for seismic effects. It is primarily historic and listed buildings with vaulted structures, or even partially damaged ones, that are exceptionally sensitive to the deformations of the supporting structure due to natural seismicity, and their response to these effects is often accompanied by the appearance of structural failures.

The growing volumes of particularly heavy truck traffic with high road pavement loading values and, in many cases, poor quality and uneven road pavement surfaces intensify the effects technical seismicity on buildings situated in the vicinity of traffic routes.

The NAKI II DG16P02M055 research project incorporates extensive experimental and theoretical research into the effect of grouting on the physical and mechanical characteristics of brick, stone and mixed masonry. The focus of the research is on the verification of particularly the reinforcing effect of selected grouting agents based on hydraulic lime (nanolime), resins and silicates. Selected materials are used for the monitoring of the effect of grouting on changes in the porosity, pore distribution, absorption capacity as compared to ungrouted masonry, and the reinforcing effect of grouting on historic brick, sandy marlstone, sandstone, trachyte, limestone and mixed masonry with a lime binder for different types of grouting agents as compared to ungrouted masonry.

Precast reinforced concrete demountable column system with elastically mounted diaphragms inserted into frame sections developed within the TACR grant project [1] was verified by a pseudo-dynamic tests in the UTAM AV CR experimental facility. The experimental verification and theoretical analysis was aimed at identifying the stiffness characteristics and dynamic response of the “frame” section, including the evaluation of the effect of demountable joints while mounting the diaphragm on beams using elastic (rubber) bearings. The experimental verification was performed for three different diaphragm to beam connections made by a rigid screw connection and by a connection with elastic bearings with two different stiffness values. During the first phase of the experimental verification the structure was exposed to pseudo-dynamic loading by a hydraulic jack controlled by deformation or by amplitude and corresponding frequency of the jack. The absolute deformations of the structure as well as relative deformations between individual structural elements were monitored by means of linear deformation sensors. The force necessary for reaching these deformations was also monitored. In the second phase of the experimental campaign the natural frequencies and dampening characteristics were identified. Based on the obtained values, the stiffness and dynamic characteristics of the frame structure with three different types of the stiffening diaphragm connections were identified and were compared with numerical model. Theoretical analysis and results of experimental research proved the satisfactory resistance of the proposed multi storey building system.

The article presents partial results of laboratory research into physical and mechanical characteristics of materials most commonly used as walling units in masonry structures of historic and heritage buildings. Core boreholes and specimens for the laboratory research of selected characteristics were sampled from accessible places of historic buildings, which had not been restored or reconstructed.The results of the research brought new knowledge about the unreliability (variance) of the properties of historical, mainly natural building materials, and, at the same time, pointed out the need for further research and extension of knowledge necessary for the assessment of residual physical and mechanical characteristics of historic masonry structures.

The article sums up the requirements for historic masonry structures whose reinforcement is based on the grouting technology application, the grouting implementation procedure in relation to the extent, type and size of masonry damage. Special focus is put on grouting agents and requirements for their characteristics.

The TA02010837 project "Multipurpose dismantleable prefabricated reinforced concrete building system with controlled joint properties and the possibility of repeated use " includes the development of a multi-purpose reinforced concrete precast system with demountable joints. The novel concept of the reinforced concrete precast structure brings numerous innovative, not yet verified solutions, construction and structural problems, functional requirements and user qualities. Apart from theoretical and numerical analyses, a component part of the research is demanding and extensive experimental research into the load-bearing system’s structural members and nodes, including the verification of the hybrid prototype implementation system in which the basic versions of the presumed system alternatives are applied – a column, pillar, wall, integrated system and a system composed of open spatial wall units.

Provedené numerické analýzy prokazují oprávněnost požadavku na posouzení důsledků dodatečného provedení otvorů ve stávající nosné panelové stěně na její napjatost a na jeho základě návrh opatření zajišťujících spolehlivé přenesení zvýšených normálových napětí v tlaku –σy, zejména v přiléhajících částech stěnové konstrukce a ve stycích stěna – strop – stěna, vodorovných napětí v tahu +σx, zejména v nově vytvořeném nadpraží a v oblasti stropních věnců nad a pod dodatečně provedeným otvorem a smykových napětí τxy zejména ve svislých stycích. Základem analýzy musí být výstižné výpočetní modely konstrukce. Provedené numerické analýzy prokazují, že napjatost nosné stěny v okolí dodatečně provedeného otvoru závisí na velikosti a umístění otvoru (např. poblíž okraje stěny) a podlaží, v němž je otvor proveden. Se zvětšující se šířkou otvoru, počtem podlaží nad nově provedeným otvorem a zmenšující se šířkou nově vzniklých stěnových pilířů narůstají všechny složky napětí. ❚ Numerical analyses demonstrate the justification of the requirement for the assessment of the impacts of creating additional openings in an existing load-bearing prefabricated wall on its stress state and, based on it, the design of measures to ensure a reliable transfer of increased compressive normal stresses –σy, especially in adjacent parts of the wall structure and in wall – floor – wall joints, horizontal tensile stresses +σx, especially in the newly created head and in the area of floor ring beams above and below the additional opening, and shear stresses τxy especially in vertical joints. The analysis must be based on accurate computational models of the respective structure. The performed numerical analyses manifest that the stress state of a loadbearing wall around the additional opening depends on the opening’s size and location (for example, near the edge of the wall) and on the storey on which the opening is made. All the stress components grow with the growing width of the opening, the number of storeys above the newly created opening and the decreasing width of newly created wall pillars.

The paper presents the results of the experimental and theoretical analysis of segmented barrel vaults unreinforced and reinforced on their surface with composite strips, exposed to alternating monotonously rising loading and dynamic loading in the horizontal and vertical direction. The results of the research manifested an increase in the ultimate loading capacity and deformation characteristics of a vault reinforced with surface applied composites. At the same time, results of the effects of masonry vault reinforcement with composites on its dynamic characteristics (natural frequencies) were obtained.

The demountable precast reinforced concrete building system consists of bar and thin-walled units allowing designing hybrid integrated systems of multi-storey buildings. The system’s characteristic property are demountable, self-rectifiable and dry joints enabling assembly without wet processes and, in case of need, the disassembly and relocation of the structure. The system applies special mounting, the joint of prestressed hollow core floor units and the load-bearing structure by steel pins additionally embedded in the hollow cores. The article presents the results of experimental research into the major parts and joints of the load-bearing system and the verification of the load-bearing system’s prototype exposed to static load tests with an example of the load-bearing system’s assembly and disassembly.