The variability of reinforced concrete beams deflections can be attributed to uncertainties in the material properties, the dimensions of the elements, the reinforcement and the applied loads. Other sources of uncertainties are the errors of the model used in the calculation procedures, the boundary conditions and the development of cracks due to shrinkage and temperature changes and uncertainty regarding the time of application of loads during construction and installation of non-structural elements. A deterministic model is employed in order to calculate the immediate and time-dependent deflections using a finite element approach. The model uses a consistent theory for the analysis of curvature and deflections of reinforced concrete beams in the cracking stage. The model considers the contribution of concrete between cracks, effect known as tension stiffening. The results of the deterministic model are compared with the test data in the literature.
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Descubra todo lo que Scribd tiene para ofrecer, incluyendo libros y audiolibros de importantes editoriales. Scuero 1 ; G.
Vaschetti 2 ; M. Gontijio 3 1 Dr. Resumo H mais de 50 anos, as geomembranas vm sendo aplicadas em todo o mundo em uma variedade de estruturas hidrulicas, incluindo todos os tipos de barragens, canais, tneis hidrulicos e reservatrios. Seu uso em barragens expandiu de projetos pioneiros na construo de barragens de terra a projetos para a reabilitao a seco e subaqutica de todos os tipos de barragens, e a construo de barragens de CCR.
O trabalho apresenta os dados de desempenho disponveis. Palavra-Chave: geomembranas impermeveis, barragens de terra e enrocamento, barragens de concreto e de CCR. Abstract Since more than 50 years, geomembrane have been applied all over the world to a variety of hydraulic structures, including all types of dams, canals, hydraulic tunnels, reservoirs.
Their use in dams expanded from pioneer projects in construction of new fill dams, to rehabilitation of all types of dams, in the dry and underwater, and to construction of new RCC dams. The paper discusses for each type of application the assets of geomembrane systems from the technical and economical point of view, and through case studies illustrates recent outstanding experiences of the state-of-the-art systems available: Silvretta 80m high gravity dam in Austria as example of a geomembrane rehabilitation system installed in two separate campaigns to minimise impact on power production, Turimiquire m CFRD in Venezuela as example of underwater rehabilitation at depth reaching 65m on a critical area of the upstream face of the dam allowing substantial reduction of seepage with no impact on exploitation of the reservoir, Sar Cheshmeh tailings dam raising in Iran and the 91m high Runcu rockfill dam in Romania as examples of a new concept for construction of fill dams with an upstream exposed geomembrane as only watertight element, Mau RCC dam in Brazil as example of an exposed geomembrane as preventive measure to avoid water infiltration in a dam just completed.
The paper presents the available performance data. Keywords: impermeable geomembranes, earthfill and rockfill dams, concrete and RCC dams. The first geomembranes applications were carried out in new embankment dams because being too permeable they often required a separate impervious element. In many cases, geosynthetic barrier systems were more economical and easier to install than traditional impervious materials such as clay, concrete, bituminous concrete [Cazzuffi et al.
Europe was a pioneer in developing the use of geomembranes in dams: the first geomembrane installations were made in at Contrada Sabetta rockfill dam in Italy, and in at Dobsina earthfill dam in Slovakia. With only two exceptions Terzaghi rockfill dam in Canada and Atbashinsk rockfill dam in Kirgikistan up to the early ies all geomembrane applications on dams were made in Europe.
Also all first applications of geomembranes on concrete dams were made in Europe [ICOLD, ]: on some arch dams in Austria in the early ies, on Heimbach gravity dam in Germany in and on Lago Miller gravity dam in Italy in In RCC dams, USA was the pioneer in the application of the covered geomembrane system Carrol Ecton , while Europe pioneered the application of the exposed geomembrane system, derived from the state-of-the-art solution for rehabilitation of concrete dams Riou dam in France, Possibly, the credibility of impervious synthetic geomembranes has been established by the good performance of embedded PVC waterstops in a very large number of concrete dams worldwide.
A geomembrane placed on the upstream face of a dam or inside a dam can be considered, from a conceptual viewpoint, as one huge waterstop sealed at the abutments, bottom and crest. In concrete dams and RCC dams, there is a state-of-the-art system that is generally used for dry installation.
The geomembrane is installed at the upstream face, it is mechanically anchored on the face, and watertight sealed at all peripheries. The state-of-the-art system has been adapted to installation on embankment dams, with the modifications required by a subgrade that can be less cohesive than concrete, and to underwater installation. These aspects are addressed in the case histories of chapter 2. The presence of a face drainage system allows continuous monitoring of the efficiency of the geomembrane liner, and leak localisation systems are available to spot the area of the leak if any.
In case of alkali-aggregate reaction, the drained geomembrane system discussed in the paper has been proven to allow dehydrating the dam of already infiltrated water, contributing to slow the reaction [Liberal et al.
In embankment dams, the geomembrane can be installed at the upstream face in exposed position, to substitute concrete slabs or bituminous concrete facings and construct what is known as a Geomembrane Face Rockfill Dam GFRD , such as described in chapter 3.
When vandalism or excessive environmental aggression falls of rocks or ice blocks are feared, the geomembrane can be covered in the areas of concern. The central position is adopted to substitute clay cores when clay is not available in the needed quantity or in presence of unsuitable environmental conditions, or can be used in place of bituminous concrete cores to facilitate and speed up construction.
The main assets of a geomembrane system in construction of new embankment dams is its capability of resisting settlements and differential movements that would destroy other types of impervious layers, the possibility of using for the fill materials of lower quality, of reducing construction times and constraints, and of avoiding the need for embedded waterstops.
In RCC dams, the geomembrane is installed upstream. The exposed system adopts the same face anchorage used for rehabilitation and is discussed in chapter 3. The main assets of a geomembrane system in RCC dams are its capability of avoiding future concerns about the watertightness of the upstream face, including lift joints, contraction joints and joints between the RCC and the conventional concrete, of bridging any cracks that should form due to thermal constraints, avoiding the risk that water can hydro-jack the lifts, of reducing design uplift.
The main dam, completed in , is 80m high upon foundations and has 4 inspection galleries. Over the last decade, frequent exposure to freeze-thaw cycles in addition to the combined action of frost, ice and seeping water, caused severe damage to the dam concrete structure which rapidly deteriorated.
Within the rehabilitation works that started in and ended in , including waterproofing and placing new concrete on the crest, treating the foundations, grouting, renewing the instrumentation and conducting rehabilitation works at the outlet and inlet valves, Illwerke took the decision of reinstating imperviousness to the dam face by an upstream waterproofing system on the main dam and on the saddle dam.
Silvretta is the first exposed PVC geomembrane project on an Austrian dam. The final design is the result of extensive research carried out by Illwerke on available rehabilitation systems, and of evaluation of performance data from previous similar applications. The selected system consists of an exposed PVC geomembrane system on both the main dam and on the saddle dam. The objectives of the system are to prevent infiltration of seepage water into the dam body, to protect the dam structure against frost and seepage water, to drain infiltration and condensation water, and to monitor the waterproofing system.
Site specific peculiarities were the bad conditions of the surface concrete, the demanding climate risk of snowfall also in summer and the particularly tight window for installation only three springtime months , which made it an extremely challenging project particularly with respect to planning and programming. The decision was taken to design the geomembrane system so as to follow the dewatering program foreseen for the general rehabilitation works.
As a result the geomembrane system was installed in two separate campaigns. During the first campaign in , water was lowered to m and the saddle dam and top part of the main dam, from m to crest, were lined, in total 12,m2.
During the second campaign in , the reservoir was totally dewatered and the remaining lower part of the main dam, in total about 5,m 2, was lined. At Silvretta, reducing execution times was essential to successfully complete the project in the allotted time. The conditions of the concrete were very bad, but extensive surface preparation was not compatible with the tight time schedule.
The use of geosynthetic materials instead of more traditional methods for surface preparation allowed minimising civil works and reducing the risk of delays due to bad weather. The geogrid also acts as a support layer to the waterproofing system over the biggest cracks in the face. Installation was carried out from 8 travelling platforms suspended at crest and, in the areas not accessible by the platforms, i.
Figures 1 and 2 - Installation of support geogrid and anti-puncture geotextile under shelter at Silvretta dam. The waterproofing liner is Sibelon CNT , a geocomposite consisting of a 2. The face anchorage system, which allows pre-tensioning the PVC geocomposite, consists of two stainless steel ribs generally referred to as profiles , the first one, U-shaped, fastened to the dam upstream face, and the second one, omega-shaped, installed over the PVC geocomposite.
The geometry of the two profiles is such that, when they are tightly connected, they secure the geocomposite to the upstream face and pre-tension it.
Pre-tensioning prevents the geocomposite from becoming loosened or wrinkled during service. Pre-tensioning is preferable [ICOLD ] for the safety and durability of the system: if the geocomposite is not adequately tensioned, the repeated loads to which it will be subjected during its service life waves and wind, varying water levels, etc. Figures 3 and 4 - Pre-tensioning profiles, and works at the main Silvretta dam in spring from right to left, surface preparation, installation of vertical profiles, installation of support geogrid the dark grey material , installation of anti-puncture geotextile the white material , installation and fastening of the PVC geocomposite the light grey material.
The submersible perimeter seals are made with 80x8mm stainless steel batten strips compressing the PVC geocomposite on a regularizing resin, with the aid of rubber gaskets and stainless steel splice plates to distribute the compression and achieve watertightness against water in pressure.
The depth of the anchor bolts for the tensioning profiles and for the watertight perimeter anchorage was based on the results of the pull-out resistance tests carried out on the face concrete.
The seal at crest was designed not to be air-tight, so as to establish atmospheric pressure in the drainage system and avoid suction. The drainage system is divided in 6 separate vertical compartments to allow monitoring the performance in sections.
Drained water is discharged in the bottom gallery by transverse discharge pipes, one pipe for each compartment. Waterproofing works of the campaign started on March 29 and were completed on June The waterproofing liner installed was temporarily sealed at about m elevation with a horizontal seal made by 50x3mm stainless steel batten strips tied with mechanical anchors at 0.
This seal was dismantled in the campaign, when the PVC geocomposite on the upper part of the dam was connected to the PVC geocomposite installed in in the lower part of the dam. In , the reservoir was totally dewatered to allow lining the main dam, from about m elevation down to the bottom. A thicker layer of mud and debris had to be removed to expose the foundation. Installation of the waterproofing system proceeded in the same way as described for the upper section. At left of the intake structure a sheltered scaffolding was installed, while at right of the intake structure installaiton was carried out from travelling platforms.
As for the campaign, this arrangement allowed organising the works so as to minimise idle time due to bad weather. Waterproofing works of the campaign started on March 16 and were completed on May In total 17,m2 in the two campaigns.
Figures 5 to 7 - At left works preparation at the main Silvretta dam in spring , at middle waterproofing works ongoing under shelter at the left of the intake and from travelling platforms at the right of the intake, at right works completed. Illwerke recognized to Carpi a bonus of 40, for completing the works in both campaigns before the contractual deadline [Scuero et al. In autumn , with reservoir at full water level, seepage at the drains was only drops, and stands unchanged until the present day.
Owned by Ministerio del Poder Popular para el Ambiente, the dam was designed by Barry Cooke and is used for potable water supply. The dam was impounded in and just after a year, leakages were observed. In , , , , and , repeated repairs were carried out with clay material and granular material of different sizes, plus a geomembrane over m2. The concrete presented scales and loss of cementitious material honeycombs in several places.
In addition there was a permeable area below the geomembrane placed in , which due to insufficient anchorage had been locally displaced and was not performing as expected. Following the very poor outcome of all repair measures adopted until then, in May the decision was taken to install an impervious polyvinylchloride PVC geocomposite at the upstream face as permanent repair measure.
The geocomposite system was to be installed at first over the most critical areas, in total about 14 m 2, from el. Less crucial areas to be lined in a subsequent phase, under a separate contract.
Most of the repair work was therefore to be carried out underwater. A contract for the design of the waterproofing system was awarded to Carpi based on the experience acquired by the company in both dry and underwater application of geomembrane systems on dams. The geomembrane system was designed to be installed over the easily accessible areas obviating the immediate need for expensive sediment removal. A design choice has been to have the same conceptual exposed geomembrane system for the dry and underwater parts.
Another design choice has been to minimize as much as possible surface preparation fissures, loss of cementitious material, large cavities, and severe roughness were present through the extensive use of synthetic materials, like at Silvretta. Two different geogrids were used for the face slabs, a standard one for the smaller cracks and a heavy duty one for the larger cracks and the cavities. A robust geocomposite was deemed necessary due to such high water head.
The geocomposite has been supplied in 2. For the underwater part, four sheets were pre-welded at site to prefabricate 7. The face anchorage system of the dry section is the same patented tensioning system of Silvretta. In the underwater section, the geometry of the profiles was modified to adapt it to the underwater environment: in dry conditions the tensioning profiles are waterproofed by a PVC geomembrane strip welded over them, in underwater conditions since welding is not feasible the profiles are modified to be intrinsically watertight.
Adequate gaskets assure even compression all along the profiles, achieving an intrinsically watertight fastening line. Figures 9 to 11 - Turimiquire: at left the face anchorage profiles and support geogrid, at middle and right the 7. The face anchorage system in the section that will be mostly covered by water has anchorage lines at 7. The geocomposite is sealed along all peripheries by a perimeter seal to avoid water infiltrating behind it.
Flávio Alberto Crispel
A utilização de geomembranas na reabilitação e construção de novas barragens