Radek Zigler

THE ANALYSIS OF NON‐STRESS EFFECTS ON HISTORICAL STONE BRIDGE STRUCTURES (MONITORING, THEORETICAL ANALYSIS, MAINTENANCE)

Abstract Due to non‐stress cyclic effects of temperature and moisture, stone bridge structures are subjected to deformations, a gradual growth of permanent deformations, crack development and subsequent disintegration of the stone masonry of bridge vaults. A theoretical analysis of the stress‐state and deformations of the stone bridge structure caused by non‐stress effects and the in‐situ monitoring of deformation changes of the breast walls and the bridge vaults of the historic structure of Charles Bridge (from the mid‐14th century) manifested a response and a growth in permanent deformations and disintegration of the stone bridge structure due to the effects of temperature and moisture. The behaviour of the bridge structure is significantly affected by the interaction of the vault bridge structure with the bridge body filler when exposed to the above‐mentioned non‐stress effects. Special attention must be paid to the spacing effect of filling layers on the stone bridge structure. When repairing historic...

Stress State Analysis and Failure Mechanisms of Masonry Columns Reinforced with FRP under Concentric Compressive Load

The strengthening and stabilization of damaged compressed masonry columns with composites based on fabrics of high-strength fibers and epoxy resin, or polymer-modified cement mixtures, belongs to novel, partially non-invasive and reversible progressive methods. The stabilizing and reinforcing effect of these fabrics significantly applies to masonry structures under concentric compressive loading whose failure mechanism is characterized by the appearance and development of vertical tensile cracks accompanied by an increase in horizontal masonry strain. During the appearance of micro and hairline cracks (10−3 to 10−1 mm), the effect of non-pre-stressed wrapping composite is very small. The favorable effect of passive wrapping is only intensively manifested after the appearance of cracks (10−1 mm and bigger) at higher loading levels. In the case of “optimum” reinforcement of a masonry column, the experimental research showed an increase in vertical displacements δy (up to 247%), horizontal displacements δx (up to 742%) and ultimate load-bearing capacity (up to 136%) compared to the values reached in unreinforced masonry columns. In the case of masonry structures in which no intensive “bed joint filler–masonry unit” interaction occurs, e.g., in regular coursed masonry with little differences in the mechanical characteristics of masonry units and the binder, the reinforcing effect of the fabric applies only partially.

The application of carbon composites in the rehabilitation of historic baroque vaults

The stabilization and reinforcement of damaged barrel vaults with lunettes over an arcaded walk, applying composite strips based on high-strength carbon fibers and epoxy resin, was performed during the restoration of a historic monastery. The application of reinforcing composite strips in the soffit of damaged barrel vaults was preceded by relatively extensive experimental research and theoretical analyses. This method significantly reduces the interventions into and the degradation of the original historic structure (surface application) and is reversible.

Strengthening of Masonry Structures Using FRP — Experimental Research

The article deals with the problems of the failure mechanism and the load-bearing capacity of masonry barrel vault structures and masonry columns strengthened with fabric of carbon fibres. The executed experimental research of the effect of strengthening segmental barrel vaults and masonry columns by carbon fabric showed a prominent growth in the ultimate bearing capacity and ductility of barrel vault structures and masonry columns. The application of carbon fabric (CFRP) in the vault area exposed to tensile stresses limited not only the appearance and development of characteristic tensile cracks at these vault cross-sections, but also significantly increased the vault stability against buckling. The position of strengthening elements — the carbon fabric (CFRP) — affected the failure mechanism of the masonry vaults and masonry columns.

Stabilization and Strengthening of Historic Buildings' Stone Masonry Columns

The experimental research of failure mechanism of stone columns made of coursed masonry of regular sandstone blocks and coursed masonry of irregular (freestone) blocks under concentric compression and the research of the performance of non-reinforced as well as CFRP-reinforced stone columns completed to-date pointed out the necessity of a different approach to the assessment of the load-bearing capacity, or residual load-bearing capacity, of masonry composed of stone blocks.

The Response of Masonry Barrel Vaults to Repetitive Static and Dynamic Loads and Example of Rehabilitation of Historic Barrel Vaults

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 Tepla (built in the 16th century), located in a seismically active region of West Bohemia.

Physical and mechanical characteristics of building materials of historic buildings

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.

Demountable Frame Structure with an Elastically Embedded Diaphragm

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.

GROUTING METHODS FOR THE REHABILITATION AND REINFORCEMENT OF MASONRY STRUCTURES DAMAGED BY CRACKS

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.

CONTRIBUTION TO THE POTENTIAL OF USING FRP MATERIALS IN THE REHABILITATION AND STABILIZATION OF TIMBERED BUILDINGS

Wooden log, timbered perimeter and interior walls ranked among the most common building constructions used from the Early Middle Ages. In most cases, the local natural resources, i.e. wood, clay, straw and stone, were used for building houses with wooden framing. This article outlines typical defects and failures of timbered houses, “classic” techniques for the rehabilitation of these defects and failures indicating the potential of using composite materials based on highstrength fibres and epoxy resin in the rehabilitation and strengthening of timbered buildings.