Ústav betonových a zděných konstrukcí

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    Strengthening of bridges by post-tensioning using monostrands in substituted cable ducts
    (IOP Publishing, 2017-09-15) Klusáček, Ladislav; Svoboda, Adam
    Post-tensioning is suitable, reliable and durable method of strengthening existing engineering structures, especially bridges. The high efficiency of post-tensioning can be seen in many applications throughout the world. In this paper the method is extended by a structural system of substituted cable ducts, which allows for significantly widening application of prestressing so it’s convenient mostly for application on beam bridges or slab bridges (built in years 1920 – 1960). The method of substituted cable ducts is based on theoretical knowledge and technical procedures, which were made possible through the development in prestressing systems, particularly the development of prestressing tendons (monostrands) and encased anchorages, as well as progress in drilling technology. This technique is highly recommended due to minimization of interventions into the constructions, unseen method of cable arrangement and hence the absence of impact on appearance, which is appreciated not only in case of valuable historical structures but also in general. It is possible to summarise that post-tensioning by monostrands in substituted cable ducts is a highly effective method of strengthening existing bridges in order to increase their load capacities in terms of current traffic load and to extend their service life.
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    Life Cycle Assessment Optimization of a Shotcrete Tunnel Lining
    (IOP Publishing, 2018-11-27) Štěpánek, Petr; Laníková, Ivana; Venclovský, Jakub
    The proposed contribution describes the formulation of the optimization design of a utility tunnel lining. The objective function is defined as a multicriterial problem and includes economic and environmental aspects associated not only with concrete member production but also with maintenance during utilization (life cycle assessment). The constraining conditions expressed by relations derived from equations of equilibrium (the solution of optimization calculations for a structure with a Winkler foundation using the Finite Element Method), the reliability conditions of a reinforced concrete structure and the continuity of deformations define the range of allowable solutions from the mathematical viewpoint. The thickness of the tunnel lining and areas of the top and bottom reinforcement in cross-sections are optimized
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    Effective Way to Reconstruct Arch Bridges using Concrete Walls and Transverse Strands
    (IOP Publishing, 2017-09-15) Klusáček, Ladislav; Pěkník, Robin; Nečas, Radim
    There are more than 500 masonry arch bridges in the Czech Road system and about 2500 in the Czech Railway system. Many of them are cracked in the longitudinal (span) direction. The barrel vaults are separated by the cracks into partial masonry arches without load bearing connection in transverse direction. These constructions are about 150 years old and they are also too narrow for the current road system. This paper presents a strengthening method for masonry arch bridges using transverse post-tensioning. This method is very useful not only for strengthening in the transverse direction, but widening of masonry arches can be taken as secondary effect especially in case of road bridges. Several bridges were successfully repaired with the use of this system which seems to be effective and reliable.
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    Stochastic optimization of reinforced concrete elements’ design
    (IOP Publishing, 2018-07-04) Venclovský, Jakub; Štěpánek, Petr; Laníková, Ivana
    Main goal of the paper is to present an algorithm for stochastic optimization of design of steel-reinforced concrete element’s cross section. Firstly, the deterministic problem is introduced and described, followed by the description of uncertainties involved in the process and stochastic reformulation of the problem. Afterwards, the algorithm itself is introduced. This algorithm is based on internal cycle of deterministic optimization using reduced gradient method and external cycle of stochastic optimization using regression analysis. The probability is assessed on orthogonal grid via modified bisection method. The paper concludes with presentation of the performed calculations and their results.
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    Transverse prestressing and reinforced concrete as the key to restoration of masonry arch bridges
    (Elsevier, 2021-08-07) Klusáček, Ladislav; Nečas, Radim; Požár, Michal; Pěkník, Robin; Svoboda, Adam
    There is still a large number of masonry arch bridges on the road and railway network. More than 80 % of arch bridges are over 100 years old so their service life has been exceeded significantly. The general focus of the paper is to show the method for strengthening and restoration of these bridges, especially if they have been damaged by longitudinal cracks. The restoration is performed using new spandrel walls from reinforced concrete stabilized by transverse prestressed cables. This paper illustrates the strengthening process with four examples of restored road or railway bridges. In addition, it includes examples of basic cable arrangements and a design of the new concrete walls, which are used as anchorage areas for transverse prestressing. The efficiency of this method will be determined using data measured during the prestressing and a load test. The measurements have shown an extremely favourable effect of the addition of horizontal prestressing within the new reinforced concrete walls. After an evaluation of the deformation of the top cross-section reduced up to 40 % of the values before strengthening.