The cover meter shall be supported with a current calibration certificate and shall be capable of detecting the presence of reinforcement and indicating the depth from the concrete surface to the nearest point on the surface of the reinforcement with an accuracy of 1mm at a depth of 25mm. 5.6.3.3.3 Limiting Compressive Stress in Strut. Furthermore, since the center of the span is a hinged structure, there is a risk that the girder on the abutment side can be lifted. Three (3) 75mm test cubes shall be taken from the first batch of material mixed, then three(3) 75mm cubes for every 100kg of material used thereafter to test for compressive strength. Curing compounds shall not be applied to construction joints unless the joint is to be roughened or sandblasted at a later date. Table 610.251 Concrete MembersMinimum Period before Removal of Formwork and Formwork SupportsSoffits of beams, soffits of decks, soffits of slabs, soffits of cantilevers, soffits of diaphragms, soffits of pier and abutment crossheads and soffits of other structural members.7 days or until such time as the concrete has reached the specified 7day compressive strength, whichever is the greater. A Concrete shall not be dropped freely from a height exceeding two metres. Fig. (ii) All reinforcement and construction joints shall be cleaned with water complying with the specification prior to casting the concrete to ensure that salt deposits are removed. These are not strictly deteriorations mechanisms in the same way as those described in previous sections. by: the ratio of spiral reinforcement to total volume of concrete core, measured out-to-out of spirals, shall not be less than: Spirals are less effective for confinement in HSC. Further information is contained in Reference 7. exceed the values specified in table 1; except for structures with section. This section will explain the historical and engineering content on why box girders are used. maintaining the same general agreement with research results and 0.100 ksi minimum compression. Concrete box girders are commonly used in the western part of the United States. These dimensional tolerances will be a basis for acceptance of the work. HPC is less permeable than conventional Cores containing steel reinforcement shall not be tested. incorporated into this article. Internal freeze-thaw damage leads to a loss of cohesion within the concrete as a result of the internal cracking. However, statically indeterminate forces occur due to temperature changes, creep and shrinkage. Sulphate and chlorideion content shall be determined by testing of hardened concrete in accordance with AS1012.20.1. (l) Exposed Aggregate Finish for Unformed Surfaces The prepared surface shall have an exposed coarse aggregate finish free from loose aggregate and laitance. stress at ultimate as a function of c. This requires Related Papers. Nominal punching shear resistance, Vn, in kips, shall be WebShrinkage of concrete is defined as the contraction due to loss of moisture. For construction of deck slabs the fixed screed supports shall be placed parallel to the longitudinal centreline of the bridge. If the value obtained from the repeat test falls within the limits given in Table610.162, the concrete represented by the sample shall be deemed to comply with the appropriate nominated mix design slump, otherwise it shall be rejected. Eventually, aggregate particles become dislodged and fall out. Where the VPV value of any one sample representing the concrete exceeds the specified maximum 28day VPV value as shown in Table610.061, the Contractor shall carry out rectification works. ineffective. However, ld shall The use of a design yield strength higher than 60.0 In the absence of more accurate data, the shrinkage coefficients tensile zone. reinforcement as concrete strength increases. The frequency shall not be less than that shown in Table610.121. (ii) Testing for Impurities Fine aggregate shall be tested for impurities in accordance with AS1141. However, this version is a very good reference for Structural Civil Engineers, Contractors, and Designers who are working with the Combinations of water adding techniques such as ponding or continuous sprinkling, or by continuous application of mist spray, retention of formwork in place and polyethylene plastic (in combination with wet hessian) shall be used to provide effective curing to the exposed surfaces of concrete of the various cast-in-place members. Benchmarking against risk management best practice how do industry average organisations compare? should be considered. 1999, 2000, and 2001 interim revisions. Type of cement: GP General purpose portland cement GB General purpose blended cement 2. HSC and if it is appropriate to assume any shape for the The maximum projection of the large aggregate shall be 6mm above the finished concrete surface. Since this friction carries some of the shear load, shear provided by the concrete may be less. Bow in precast parapet units and new jersey barriers shall not exceed 3mm. Consequently, the Cracks can be quite large (2-4mm) and run through the full depth of the section. Concrete above deck shall not be placed until the deck formwork or the falsework for the span has been released and/or any posttensioning and grouting operations are completed. compression shall not be less than: The basic development length, ldb, may be multiplied by Academia.edu no longer supports Internet Explorer. The clay and fine silt levels of natural sands shall be monitored as a routine quality control measure and records shall be available for review by the Superintendent. 4.8.1 General. Much of this can come from the biomass of the tree itself, but that requires investment in plant, which is not always possible in an industry that is widely distributed among many small producers. Further information is contained in Reference 3. ali alshahir. Charts shall not be removed from any recording thermometers, nor the recording thermometers disturbed or moved in any way until after the removal of the steam covers. Generally, HSC has lower creep and similar shrinkage values Post-tensioning is used for balanced cantilever bridges. Concrete bar chairs and spacers shall comply with the requirements of Clauses610.26 and 610.29(f). [Equation 50], (5.7.4.2-1) (d) Moisture Content of Aggregates The moisture content of the fine and coarse aggregates shall be determined prior to concrete production for the day and whenever conditions change or fresh aggregates are delivered. The factored shear resistance, Vr, in the pier shall be splice.. Cement: Material complying with the requirements of AS3972 and as specified in this section. taken as: The equations in this article should be verified for use with HSC. reinforcement, s, shall not be less than either that 2016 The Authors. Concrete Cover: Distance between the outside of the reinforcing steel and the nearest permanent surface of the concrete member excluding any surface finishing material. HSC. ACTION: Revisions to allow higher design yield strengths are Pedestals shall be cured in accordance with the requirements of Clause610.23. extensively modified in the ACI 318-95 provisions, with Thus, 1.33 times the Impact of deterioration on the safety of concrete structures what can designers do to minimise risk? The Contractor shall take measures to protect the freshly placed concrete from rain. Upper surfaces of concrete bearing pedestals shall have a Class2 surface finish. contract documents. B1 B2 Pages: 754. [Equation 73], (5.8.4.1-3) Driers (i.e.drysand, cement or stone dust) shall not be used to absorb free water. prestressing strands shall be the same as for reinforcing steel. But when the seismic design is considered, the horizontal force may become too excessive to be covered by the support, which can be effectively addressed using stoppers or seismic isolation supports. Cylinders shall be transported to the testing laboratory in moisture proof containers. 610.20 CONSTRUCTION JOINTS AND BONDING OF NEW CONCRETE The location and details of construction joints shall be as shown on the drawings. Typically, this is either heat-cured precast sections or massive in situ sections with high cement contents. (iv) Effective Size of Coarse Aggregate Concrete in various parts of the structure shall contain coarse aggregate with the following effective maximum sizes: Joint and pedestal concrete 14mm Precast concrete 14mm for minimum cover of 25mm 20mm for minimum cover greater than 25mm All other concrete 20mm The effective minimum size will be 10mm for crushed material and 5mm for rounded materials. The nominal shear resistance, provided by the concrete in the joint The Contractor shall ensure that arrangements for the supply of concrete are made with the concrete supplier at the commencement of the Works, to ensure that a fully compliant concrete mix design which is supported with all required test results meets the specified time frames of this section. recent data. The reaction product occupies more space than its components. lower coefficient of variation than conventional concrete. Also the rate of loss of temperature under the steam covers after shutting off steam shall not exceed 30C per hour. State. Consideration may be given by the Superintendent to approve the use of fine aggregate with grading outside the specified limits if objective documented evidence is provided that concrete made with such fine aggregate grading complies with all other requirements of this section both in the fresh and hardened state, including evidence of acceptable performance regarding tendency for segregation, bleeding, plastic shrinkage, satisfactory compaction and finishing properties. Reinforcement supports and spacers shall be in accordance with Clause610.29(f). Only whole bags of material shall be used. (c) Placing Concrete in Bored Piles, Under Water and in Dry Bores The Contractor shall submit the procedure for placing concrete in bored piles, under water and in dry bores, for review by the Superintendent at least four weeks prior to concreting. The equations need to be modified to include creep and The scope should be extended to concrete strengths higher than 70 For lightweight concrete, loss of prestress shall be based on the representative properties of the concrete to be used. (g) Concrete Structures in Marine and other Saline Environments Concrete structures located in marine and other saline environments shall be constructed in accordance with the minimum compliant cementitious material options as shown in Table610.072. (15) The stress-strain behavior of Generally, the larger the concrete sections, and the higher the cement content and placing temperature, the more heat that is generated. Consequently, a separate review of the LRFD specifications was not undertaken. In addition, the vertical and horizontal alignment between adjacent segments shall not exceed5mm. Conceptual diagram of single fixed supported balanced cantilever bridge. Consideration should be given to Segments incorporating a transverse diaphragm shall be cast monolithically with the full cross section of the webs, floor and deck slab extending a distance of at least five metres from the face of the diaphragm. For normal-weight concrete, the 90-day strength of slow-curing concretes may be estimated at 115 percent of their 28-day strength. (m) Maturity Testing and Temperature Matched Curing (TMC) for Estimating the InSitu Strength of Concrete Further to the requirements of Clause610.16(d) and Clause610.16(e) various types of maturity testing and TMC may be used to determine the early age insitu strength development of concrete over a required time period for the purpose of facilitating early formwork removal, lifting precast units out of moulds or early application of loading, subject to the approval of the Superintendent. sectional area of rectangular hoop reinforcement required by The class of lap splice required for deformed bars and deformed When the average air temperature during the specified periods of curing falls below 10C, the periods of curing shall be extended by 2days. 5.7.2.2 is used and for which fpe is not less than 0.5 Water shall be sprayed under the sheeting at the edges and at laps on the day after placing concrete and at regular intervals to maintain moist conditions. The size of ducts shall not exceed 0.4 times the least gross Concrete Grade: A grade of concrete with a specified minimum cementitious material content, a maximum W/C ratio and a minimum compressive strength at 3, 7 and 28days. Only hoses connected to a functioning and accurately calibrated slump stand water meter shall be used to add water to the freshly mixed concrete in the agitator drum. The Contractor shall implement quality procedures and undertake the works in a manner which minimises the effects of traffic induced vibrations, differential deflections and stresses on the new deck widening and in the vicinity of the stitch pour and staged deck overlay, including: (a) adverse effects on the bond between the steel reinforcement and the fresh concrete (b) development of any voids between the steel reinforcement and fresh concrete (c) adverse effects on the mechanical bond at the joint interface (d) adverse effects on bonded anchors if they are used in accordance with Section680 (e) cracking during the early hardening and strength developing period. For determining the factors specified in Articles 5.11.2.1.2 and over-reinforced. increase, especially at very high compressive strength levels. ! ACTION: A revision to use the actual value of n is specified either herein or in Article5.12.4. (ii) Light Finish sandblasting shall expose the fine aggregate with occasional exposure of coarse aggregate. Eccentricity: The distance between the resultant of an applied load and the centroidal axis of the masonry element under load. point of critical section to outermost cross wire shall be taken The loss in load-carrying capacity results from both the loss in concrete section (due to spalling) and the loss in reinforcement section due to corrosion. A lower transfer length is (b) Placing All steel reinforcement shall be securely held with the correct tie wire during placing and compacting of the concrete. Element models of the construction stage. Also, HSC has less lateral expansion than conventional strength concrete, so the effect of confinement is less. (i) Concrete surfaces extending between 0.5m below the low water level and 0.5m above the high water level An epoxy protective coating shall be applied to all exposed surfaces of concrete extending between 0.5m below the low water level and 0.5m above high water level. The high temperatures in hot countries can exacerbate this. The Contractor shall develop and implement a site sampling and testing procedure in accordance with the minimum frequency requirements of this section for assurance of concrete quality, and shall ensure that records are available for review by the Superintendent. Placing of concrete in bored piles, underwater or in a dry bore shall be carried out in one continuous operation by tremie methods in accordance with Section606. Strength in excess of 3.50 ksi at the time of prestress. The cracking parallel to the exposed surface is of particular concern as it will be parallel to and close to the reinforcement. 610.11 AGGREGATES (a) General Fine and coarse aggregate for concrete shall comply with the requirements of AS2758.1. 5.13.2.4.2 Alternative to Strut-and-Tie Model. (vi) Curing of Test Cylinders Concrete test cylinders shall be placed in the heating box which is connected into the mould heating system as soon as the curing starts and shall remain in position until the curing cycle is complete. (b) Formwork Removal Times Formwork and formwork supports shall not be disturbed or adjusted during the concreting operation and shall remain in position and undisturbed until the minimum removal times given in Table610.251 have elapsed, after completion of the placing of concrete. shrinkage that are based on the recommendations of ACI Committee (ii) Screeding of Exposed Surfaces Immediately after placing and compaction, exposed surfaces other than decks and slabs shall be screeded off to the specified levels and finished with a wooden float to an even uniform surface. Concrete shall not be incorporated into the works if its consistency is outside the acceptable limits as specified in Clause610.16(c). W" ztzt The outer layers will try to contract more than the inside. The design loads for the balanced cantilever bridge design shall be those specified in the design standards for each country. of drying. (a)Vertical faces of members when height of each day's cast is:3 days(i)Columns 4 to 7 metres(ii)Walls 2 to 4 metres(b)Vertical faces of beams and pier and abutment crossheads(c)Vertical faces of pad footings.Vertical faces of members when height of each day's cast is:2 days(i)Columns less than 4 metres(ii)Walls less than 2 metresSides of slabs and piles.1 dayWhere TypeGB cement is used, the times for removal of formwork and formwork supports shall be increased by 1day. The alkali-silica reaction (ASR) involves the reaction between hydroxyl ions in the pore water and disordered silica in the aggregate. Loss of bond between steel and concrete is a result of cracking along the line and a reinforcing bar. Vibration shall not be applied either directly or through the reinforcement to any concrete which has taken its initial set Concrete decks or slabs shall be compacted by internal vibrators and vibrating screeds such that uniform consolidation is achieved throughout the deck and slab area. Bleeding and settlement, aggravated by incomplete compaction, can lead to plastic settlement cracking. The balanced cantilever bridge is a prestressed girder bridge and refers to a bridge constructed using the balanced cantilever method. This was caused by a combination of overload and low strength concrete. WebAbstract. This is inconsistent with the traditional higher coefficient than 0.24 is possible for HSC. bridge girders. The tensile stress limit in the last paragraph should be conventional concretes. equation 5.7.3.1.1-3. section. Fitments and embedments shall be located with sufficient accuracy to prevent any misfit or misalignment between mating components. Curing compounds shall not have a deleterious effect on the concrete or stain the surface of the concrete. When supported bridges are constructed using the cantilever method, there are disadvantages such as the need to additionally install temporary fixing devices to resist unbalanced moments generated during construction and constantly getting maintenance checks for the supports of the bridge during its public use. Partially articulated balanced cantilever bridge: central hinge type. investigated for its applicability with HPC. The loss in load-carrying capacity results from both the loss in concrete section (due to spalling) and the loss in reinforcement section due to corrosion. WebAll mortar fins shall be tooled away to expose a surface of dense sound concrete. B1 B2 Pages: 754. the proposed aggregate. [Equation 107], (5.14.5.3-1) Cover for metal ducts for post-tensioned tendons shall not be less Individual results shall not differ from the mean by more than15%. No waiting. In pretensioned concrete, the four major sources of prestress losses are elastic shortening (ES), creep (CR), shrinkage (SH) and relaxation (RE). ACTION: None. 4.8.2 Forces on connections. Furthermore, some HSCs have a unit weight greater than 2.48 610.38 EFFECTS DUE TO CONSTRUCTION ACTIVITIES AND GROUND VIBRATION ON FRESHLY PLACED CONCRETE The Contractor shall implement adequate precautions and manage construction activities to prevent the disturbance of formwork or transmit vibrations through to recently cast concrete or projecting steel reinforcement. Random and aligned cracks can occur with widths of up to 10mm. ' ! reinforcement to strengthen the core to offset the loss of strength wire in tension shall be limited range of ultimate creep and shrinkage coefficients. (18) Action shall be taken where levels exceed normal consistency limits derived from routine quality control testing. ACTION: A revision to remove the 70-MPa (10.0-ksi) [Equation 108], Page Owner: Office of Research, Development, and Technology, Office of Infrastructure, RDT, Topics: research, infrastructure, structures, Coordinating, Developing, and Delivering Highway Transportation Innovations, Chapter 3, Compilation and Evaluation of Results From High-Performance Concrete Bridge Projects, Volume I: Final Report. WebEnter the email address you signed up with and we'll email you a reset link. (c) Trial Mix In the absence of recent documentary evidence that the concrete mix design complies with the requirements of this section, a trial mix shall be undertaken in accordance with AS1012.2. By continuing you agree to the use of cookies. 610.16 CONCRETE CONTROL, SAMPLING AND TESTING (a) General All concrete shall be sampled and tested in accordance with AS1012 unless otherwise specified in this section. WebDear Customer: Recently, we were made aware of some technical revisions that need to be applied to the AASHTO LRFD Bridge Design Specifications, 6th Edition. The validity of this article needs to be verified for be sure that they are applicable to HSC. Vn, in kips, shall be taken as: The wall thickness of cylinder piles shall not be less than 5.0 Are skyscrapers in timber a good use of this natural resource, or are there other aspects of civil and structural engineering, or large-scale infrastructure, that would be a better use of wood? Fly ash, ground granulated blast-furnace slag, and metakaolin Thus, both the mechanical and the durability rules in the code may be invalid and the assumptions regarding service life may be over optimistic. as the lesser of: This article provides a maximum limit on the nominal shear Vn. Concrete which has begun to stiffen shall not be used in the works. Cylinders shall be transported in moisture proof containers. Please replace the existing text with the corrected text to ensure that your edition is both accurate and current. sand-lightweight provisions when partial sand replacement is used. Creep refers to a phenomenon in which the internal strain increases when a constant load is applied to the structure for a long period of time. Cracking results when the restrained plastic contraction exceeds the tensile strength of the concrete. No water shall be added after the commencement of discharge of concrete. Construction Health and Safety & CDM 2015, Structural Safety and Service Life of Concrete Structures. compressive strength. Equation 5.13.2.5.5-3 should be verified for use with HSC. 5.7 DESIGN FOR FLEXURAL AND AXIAL FORCE EFFECTS. splice.. However, the or the Balanced Cantilever Bridge. Should the average expansion of the mortar bars exceed 0.1% at 21days in the case of coarse aggregates and 0.15% at 21 days in the case of fine aggregates, the aggregates will be classed as reactive and either new aggregates shall be proposed for use and retested for compliance, or if it is proposed to use aggregates that have been classed as reactive, all of the following requirements shall be satisfied: the concrete mix be designed such that the alkali content does not exceed 2.8kg/m3 (Na2Oequivalent) a blended cement be used in the concrete mix that satisfies the minimum requirements of Table610.112.
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