CIVIL 3811 Lecture Slides - Week 3 - 2022 PDF

Introduction to Detailing in Reinforced Concrete Members CIVIL 3811/8811/9811 School of Civil Engineering | Faculty of Engineering THE UNIVERSITY OF SYDNEY The University of Sydney Page 1 What’s in concrete Concrete essentially consists of sand, cement, aggregate, and water The...

Introduction to Detailing in Reinforced Concrete Members CIVIL 3811/8811/9811 School of Civil Engineering | Faculty of Engineering THE UNIVERSITY OF SYDNEY The University of Sydney Page 1 What’s in concrete Concrete essentially consists of sand, cement, aggregate, and water The ratio between these and the types of aggregate form a balance between strength, shrinkage, and workability Additives (or admixtures) can be introduced into the mixture to: Increase workability (e.g. plasticisers) Decrease shrinkage Speed up or slow down the curing time Inhibit reinforcement corrosion As a result of this complexity, the “mix design” is usually carried out by a specialist concrete technologist Structural design engineers provide a “performance specification” The University of Sydney Page 2 Performance specification vs. mixed design Performance specifications – specifying the minimum structural requirements Strength Shrinkage Elastic modulus Slump Mix design – specifying the “ingredients” of a concrete mix All of the above, plus; Curing time Time to reach design strength Workability The University of Sydney Page 3 Procuring concrete Engineers will provide a performance specification A mixed design is created for this performance specification by the concrete supplier The builder will place an order for the correct amount of concrete on a particular day The concreters will set up a pump on site Concrete trucks will start arriving, and a hose is used to place this concrete Concreters will vibrate this concrete in place, which removes air bubbles The concrete will cure over the following weeks Concrete samples from the pour get tested for strength, generally at 7 and 28 days The University of Sydney Page 4 Pumping concrete – mobile pumps Truck-mounted pump that unfolds and delivers concrete Very heavy – requires a good “working platform” Limited access to tall buildings http://iminco.net/experienced-concrete-pump-operator-fifo-windsor-qld/ The University of Sydney Page 5 Pumping concrete – tower boom pumps For high-rise buildings, these pumps rise with the building similar to a crane They are fed from the ground floor of the building off the street https://www.milop.com.au/ The University of Sydney Page 6  Concrete trucks Concrete trucks (or concrete agitators )are filled with concrete in the batching plant and drive out to the site There is a maximum elapsed time for concrete deliveries – the distance from the batching plant to the site is important Each truck holds around 6-8 metre cube of concrete The University of Sydney Page 7  What is the maximum pouring height for a long column to be cast monolithically? Usually, 1.5m free fall is allowed for concrete. If you want to cast a column more than 1.5m high, then there are 2 options depending on the size of the column. If the concrete is done using a concrete pump, then the flexible hose attached to the end of the pump can be taken inside the column to compensate for the free fall height of the concrete. The University of Sydney Page 8 CONCRETE SEGREGATION Segregation of concrete is the separation of ingredients in concrete. As concrete is a non-homogeneous material, inappropriate mixing is the leading cause of segregation. This happens during transporting, handling, and placing of concrete. This phenomenon impacts the concrete properties. The strength of concrete reduces and results in cracking. Consequently, it should be mixed properly before use in construction. https://www.constructioncost.co/segregation-in-concrete.html The University of Sydney Page 9 Compacting concrete Freshly poured concrete has a lot of air bubbles in it, particularly in columns and walls due to their height These bubbles need to come out or you end up with “honeycombing” This process is called compaction, and usually is performed by plunging a “vibrator” into the wet concrete during the pour. The action of these vibrations allows the release of air bubbles to the Surface. https://theconstructor.org/practicalguide/ honeycombs-in-concrete-and-remedies/6889 The University of Sydney Page 10  Pouring, compacting and finishing concrete https://www.forconstructionpros.com/concrete/equipmentproducts/article/12113 148/concrete-consolidation-tips-for-choosing-the right-vibrator-type-for-the- application The University of Sydney Page 11 Finishing concrete Concrete slabs are finished to a level – measured using surveying procedures – with the use of a “float” A float is a piece of timber or steel used to make sure the concrete is flat Different finishes are available, such as: Trowel finish – finished with a steel trowel, very common if the slab is going to be covered with tiles, carpet, etc. Burnished finish – finished with a rotating steel blade to a sheen, common in industrial buildings and carparks Broom finish – raked to have a rough surface, used for outdoor footpaths and car ramps for slip resistance in the rain. https://carrollsbuildingmaterials.com/diy-concrete-placing-finishing-curing/ The University of Sydney Page 12 Curing and testing concrete Curing concrete happens over the process of a few days and weeks following the pour – it is a chemical reaction that takes the concrete from a plastic state to a solid state. Care must be taken on-site to allow the concrete to cure correctly Testing is performed on concrete samples to ensure that the correct strength and other specified properties have been achieved. The University of Sydney Page 13  Terminology Bar Individual bars, supplied in bundles to the site Range in diameter from 10mm (N10) to 100mm (N100) Generally, N12 to N36 are standard, others are fairly rare Mesh Small bars (wires), welded together to form a sheet Can be either a “square” mesh (S) or “rectangular” mesh (R) Specified as diameter and spacing, e.g. SL72 is 7mm wires at 200mm centres SL101 is 10mm wires at 100mm centres RL818 is 8mm bars at 100mm centres in one direction,8mm bars at 300mm centres in the other direction Bar is much more common than mesh The University of Sydney Page 14  Deformed bar and mesh https://www.reozone.com.au/reinforc ing-bar/deformed-reinforcing-bar/ https://www.reozone.com.au/reinforcing-mesh/ The University of Sydney Page 15  Basic purpose There are many purposes and types of reinforcement Reinforcement is generally a “deformed” steel bar that is used to tie together cracks in concrete These deformities help to bond the reinforcement with the concrete Types of reinforcement N – normal ductility, most common L – low ductility, used mostly in mesh The University of Sydney Page 16  Placing reinforcement Reinforcement is placed by a “steel fixer” on or in the slab, beam, column or wall formwork A certain “cover” is specified by the engineer – this is the distance from the face of the reinforcement to the face of formwork that will Eventually, be an exposed concrete surface Ranges from 20mm to 75mm, depending on the exposure. E.g. a surface inside an air-conditioned, dry building may only require 20mm cover, whereas if it’s exposed to salt spray from a beach may require a 45mm cover Reinforcement is fixed together with “tie wire”, steel wire that is looped around two bars and wrapped together to tighten Cover is maintained with the use of “chairs”, small steel or plastic objects that support the reinforcement a fixed distance away from the formwork The University of Sydney Page 17  Placing reinforcement Exposure classifications are defined in AS3600. For example, A1 is for internal surfaces and B1 is for external surfaces at least 1km away from the coast. The concrete cover protects the reinforcement from exposure to an environment that would cause corrosion The University of Sydney Page 18  Placing reinforcement The University of Sydney Page 19  Placing reinforcement - order Reinforcement is placed in a certain order, usually: Ties Bottom reinforcement Top reinforcement Doing this out of order makes it very difficult/impossible to place the correct reinforcement The University of Sydney Page 20  Procuring reinforcement An engineer generally specifies the size and spacing of reinforcement – for example, N12- 200 means 12mm normal ductility bars at 200mm spacing The University of Sydney Page 21  Procuring reinforcement More abbreviations are added to the end of these specifications for convenience, e.g.: EW – Each Way (used in slabs) EF – Each Face (used in walls) T+B – Top and Bottom (used in slabs and beams) NF – Near Face (used in walls) FF – Far Face (used in walls) V/Vert. – Vertical H/Horiz. – Horizontal A mat of reinforcement in a slab may therefore be specified as N12-200 EW T+B The University of Sydney Page 22  Procuring reinforcement The below specification is not sufficient for manufacturing reinforcement – there are not enough dimensions A reinforcement scheduler then uses these specifications to generate a reinforcement schedule or “bending” schedule, which specifies how the exact lengths and bends required for the reinforcement The University of Sydney Page 23  Procuring reinforcement Each bar or “bundle” of bars is tagged and delivered to the site for placement https://www.basiccivilengineering.com/2016/06/preparing-bar-schedule-manualy.html The University of Sydney Page 24  Identification and Notations D500N16-L-23-200T D500N16-L-23-200T N16-200T Top/bottom D500N16-S-35-175B spacing Bar shape code Bar shape Bar diameter Ductility class N or L Grade of steel 500 MPa Deformed bars The University of Sydney Page 25  Identification and Notations Shape codes – AS 1100:501 The University of Sydney Page 26  One-way or Two-way Slabs Deemed-to-comply Arrangement X D500N16-L-23-200T Y N16-200T D500N16-S-35-175B Reinforcement in primary direction Reinforcement in primary direction (as calculated) (as provided) bottom reinforcement top reinforcement The University of Sydney Page 27  One-way or Two-way Slabs Deemed-to-comply Arrangement X Y Reinforcement in secondary direction Reinforcement in secondary direction (as calculated) (as provided) The University of Sydney Page 28  One-way or Two-way Slabs Anchorage at Supports Nominal distance The University of Sydney Page 29  One-way or Two-way Slabs Anchorage at Supports The University of Sydney Page 30  One-way or Two-way Slabs Deemed-to-comply Arrangement Primary direction ( Negative moment reinforcement) The University of Sydney Page 31  One-way or Two-way Slabs Deemed-to-comply Arrangement Primary direction (both negative and positive moment reinforcement) The University of Sydney Page 32  One-way or Two-way Slabs General Procedure Shift the bending moment envelope by a 𝐷𝐷 distance “𝐷𝐷” Greater of 𝐷𝐷 or 12 𝑑𝑑𝑏𝑏 𝐷𝐷 Point of contraflexure Clause 9.1.3.1 (i) Not less than one third of the total negative moment reinforcement required at a support shall be extended a distance, greater of 12𝑑𝑑𝑏𝑏 or 𝐷𝐷 beyond the point of contraflexure. The University of Sydney Page 33  One-way or Two-way Slabs General Procedure Anchorage at simply supported end 𝐴𝐴𝑠𝑠𝑠𝑠,𝑟𝑟𝑟𝑟𝑟𝑟.(𝑚𝑚𝑚𝑚𝑚𝑚 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠) Clause 9.1.3.1 (ii) No shear reinforcement is required for the slab , If all reinforcement extend beyond the support - 4 𝒅𝒅𝒃𝒃 If only half of the reinforcement requirement at mid-span extended beyond the face of the support -8 𝒅𝒅𝒃𝒃 If shear reinforcement is required , At least half of the total positive reinforcement required at mid-span shall be extended for a distance, greater of 12 𝒅𝒅𝒃𝒃 or 𝑫𝑫 from the face of the support. The University of Sydney Page 34  One-way or Two-way Slabs General Procedure Anchorage at a continuous or a restrained support 𝐴𝐴𝑠𝑠𝑠𝑠,𝑟𝑟𝑟𝑟𝑟𝑟.(𝑚𝑚𝑚𝑚𝑚𝑚 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠) Min. 25% 𝐴𝐴𝑠𝑠𝑠𝑠,𝑟𝑟𝑟𝑟𝑟𝑟.(𝑚𝑚𝑚𝑚𝑚𝑚 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠) Clause 9.1.3.1 (iii) Not less than one quarter of the total positive moment reinforcement required at mid-span [𝐴𝐴𝑠𝑠𝑠𝑠,𝑟𝑟𝑟𝑟𝑟𝑟.(𝑚𝑚𝑚𝑚𝑚𝑚 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠) ] shall continue past the near face of the support. The University of Sydney Page 35  One-way or Two-way Slabs Additional Requirements for Two-way Slabs Clause 9.1.3.3 The arrangement shall apply to each direction. When a simply supported or continuous slab is not square, the arrangement shall be based on the shorter span. For continuous slab with unequal shorter spans the extension of negative moment reinforcement beyond each face of a common support shall be based on longer of the shorter spans. In the case of a two way slab, it is possible to reduce the length adopted for negative moment at a discontinuous edge to 0.15 times the shorter span. The University of Sydney Page 36  Beams Deemed to Comply Method 𝐴𝐴𝑠𝑠𝑠𝑠,𝑡𝑡𝑡𝑡𝑡𝑡,𝑠𝑠𝑠𝑠𝑠𝑠 1 50% 𝑜𝑜𝑜𝑜 𝐴𝐴𝑠𝑠𝑠𝑠,𝑡𝑡𝑡𝑡𝑡𝑡,𝑠𝑠𝑠𝑠𝑠𝑠 1 0.3𝐿𝐿𝑛𝑛 0.3𝐿𝐿𝑛𝑛 25% 𝑜𝑜𝑜𝑜 𝐴𝐴𝑠𝑠𝑠𝑠,𝑡𝑡𝑡𝑡𝑡𝑡,𝑠𝑠𝑠𝑠𝑠𝑠𝑠 0.3𝐿𝐿𝑛𝑛 0.2𝐿𝐿𝑛𝑛 0.2𝐿𝐿𝑛𝑛 or min 2N12 𝐴𝐴𝑠𝑠𝑠𝑠,𝑡𝑡𝑡𝑡𝑡𝑡,𝑠𝑠𝑠𝑠𝑠𝑠 2 𝐴𝐴𝑠𝑠𝑠𝑠,𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏,𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 0.1𝐿𝐿𝑛𝑛 0.1𝐿𝐿𝑛𝑛 0.1𝐿𝐿𝑛𝑛 25% 𝐴𝐴𝑠𝑠𝑠𝑠,𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏,𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 Support 1 Support 2 AS 3600-2018/Clause 8.3.1.5 The University of Sydney Page 37  Anchorage Requirements Development Length In order to make sure there is a sufficient bond between reinforcement and concrete, adequate anchorage is provided for the flexural reinforcement. If a reinforcing bar is at yield in a region of a member, for an example as in a critical section of a footing or a slab, then the bar must be extended to a sufficient distance (𝐿𝐿𝑠𝑠𝑠𝑠,𝑡𝑡 ).This is done on either side of this region to allow the force to be transmitted from the bar to the surrounding concrete. Critical section Bond stress The University of Sydney Page 38 Anchorage Requirements Basic Development Length The basic development length of a deformed bar in tension is calculated from 𝟎𝟎. 𝟓𝟓𝒌𝒌𝟏𝟏 𝒌𝒌𝟑𝟑 𝒇𝒇𝒔𝒔𝒔𝒔 𝒅𝒅𝒃𝒃 𝑳𝑳𝒔𝒔𝒔𝒔.𝒕𝒕𝒕𝒕 = ≥ 𝟐𝟐𝟐𝟐𝒌𝒌𝟏𝟏 𝒅𝒅𝒃𝒃 AS 3600-2018/Clause 13.1.2.2 / 𝒌𝒌𝟐𝟐 𝒇𝒇𝒄𝒄 where, 𝑘𝑘1 = 1.3 for bars with more than 300 mm concrete cast below the bar. 𝒌𝒌𝟏𝟏 = 1.0 for bars with less than 300 mm concrete cast below the bar. 𝒌𝒌𝟐𝟐 = (𝟏𝟏𝟏𝟏𝟏𝟏 − 𝒅𝒅𝒃𝒃 )/𝟏𝟏𝟏𝟏𝟏𝟏 𝟎𝟎. 𝟏𝟏𝟏𝟏 𝒄𝒄𝒅𝒅 − 𝒅𝒅𝒃𝒃 𝒌𝒌𝟑𝟑 = 𝟏𝟏. 𝟎𝟎 − 0.7 ≤ 𝑘𝑘3 ≤ 1.0 𝒅𝒅𝒃𝒃 𝑑𝑑𝑏𝑏 = diameter of the bar 𝑐𝑐𝑑𝑑 is the smaller of the concrete cover to the bar or half the clear distance to the next parallel bar. (refer to the next slide) The University of Sydney Page 39  Anchorage Requirements Refined Development Length Refined development length incorporate the positive affect from the transverse reinforcement. 𝐿𝐿𝑠𝑠𝑠𝑠,𝑡𝑡 = 𝑘𝑘4 𝑘𝑘5 𝐿𝐿𝑠𝑠𝑠𝑠,𝑡𝑡𝑡𝑡 𝑘𝑘4 , allows for the positive effect on anchorage of the effective area 𝜆𝜆 of any transverse reinforcement within the development area. 𝑘𝑘4 = 1.0 − 𝐾𝐾𝐾𝐾 0.7 ≤ 𝑘𝑘4 ≤ 1.0 𝐾𝐾 allows for the location of the transverse steel relative to the bar being anchored. 𝐾𝐾 = 0.05, if transverse steel provided in the cover side closer to the surface 𝐾𝐾 = 0, where transverse steel provided in inner side and is ineffective. The University of Sydney Page 40  Anchorage Requirements Refined Development Length (a) Horizontal splitting due to (b) Vertical splitting due to (c) Splitting (bond) failure at insufficient bar spacing insufficient cover a lapped splice The University of Sydney Page 41  Anchorage Requirements Development Length Clause 13.1.2.4- The development length (𝐿𝐿𝑠𝑠𝑠𝑠 ) to develop a tensile stress (𝜎𝜎𝑠𝑠𝑠𝑠 ), less than the yield strength (𝑓𝑓𝑠𝑠𝑠𝑠 ), shall be calculated from - 𝜎𝜎𝑠𝑠𝑠𝑠 𝐿𝐿𝑠𝑠𝑠𝑠 = 𝐿𝐿𝑠𝑠𝑦𝑦,𝑡𝑡 𝑓𝑓𝑠𝑠𝑠𝑠 but shall be not less than- (a) 12 𝑑𝑑𝑏𝑏 (b) For slabs, as permitted by clause 9.1.3.1(a)(ii) The University of Sydney Page 42  Standard Details Standard Hooks and Cogs (a) 1800 hook (b) 900 cog The standard hook or cog is considered to provide a little over 50% of the development length. dp is the pin diameter and a, b, and c are given in the slide (22). (c) 1350 hook The University of Sydney Page 43  Standard Details Standard Hooks and Cogs (c) 1350 hook (b) 900 cog The University of Sydney Page 44  Standard Details Standard Hooks and Cogs Minimum lengths of bars required to form a standard hook or cog The University of Sydney Page 45  Standard Details Lap Splices for Bars in Tension Reinforcement available in certain fixed lengths (6m, 9m, 12m etc). Also due to dimensional and constructional requirements, reinforcement need to be terminated at certain distances. In order to continue the reinforcement cage beyond the terminated point it is required to provide a lap between connecting bars. The lap length should be able to transfer the stresses from one bar into the other. The University of Sydney Page 46  Standard Details Lap Splices for Bars in Tension The tensile lap length (𝐿𝐿𝑠𝑠𝑠𝑠.𝑡𝑡.𝑙𝑙𝑙𝑙𝑙𝑙 ) for either contact or non-contact splices shall be calculated from – (Clause 13.2.2) 35-40𝑑𝑑𝑏𝑏 for general 𝐿𝐿𝑠𝑠𝑠𝑠.𝑡𝑡.𝑙𝑙𝑙𝑙𝑙𝑙 = 𝑘𝑘7 𝐿𝐿𝑠𝑠𝑠𝑠.𝑡𝑡 ≥ 0.058𝑓𝑓𝑠𝑠𝑠𝑠 𝑘𝑘1 𝑑𝑑𝑏𝑏 applications 𝒌𝒌𝟕𝟕 shall be taken as 1.25, unless As provided is at least twice As required and no more than one‐half of the tensile reinforcement at the section is spliced, in which case k7 = 1. In narrow elements or members (such as beam webs and columns), the tensile lap length (Lsy.t.lap) shall be not less than the larger of 0.058𝑓𝑓𝑠𝑠𝑠𝑠 𝑘𝑘1 ,k7 Lsy.t and Lsy.t+1.5sb. where sb is the clear distance between bars of the lapped splice. If 𝑠𝑠𝑏𝑏 < 3𝑑𝑑𝑏𝑏 consider 𝑠𝑠𝑏𝑏 = 0 The University of Sydney Page 47  Openings in Slabs Small Openings An opening with dimensions less than 300 mm x 300 mm Bars removed Bars added The University of Sydney Page 48  Openings in Slabs Larger Openings Opening size between 300 mm x 300 mm and 1000 mm x 1000 mm Bars stopped / moved Bars added The University of Sydney Page 49  Openings in Slabs Openings in Slabs – Adjacent to a Beam Bars stopped Bars added The University of Sydney Page 50  Standard Details Openings in Slabs – Adjacent to a Beam Bars stopped Bars added The University of Sydney Page 51  Footings Reinforcement Details Clause 13.2.4 3 fitments present Clause 10.7.4.3 over the lap length The University of Sydney Page 52  Columns Standard Details 4-N20 R10-250 4-N20 Clause 10.7.4.3 Clause 10.7.4.3 The University of Sydney Page 53  Columns Column Schedule Column Types Column mark Footing detail Footing levels The University of Sydney Page 54 Lateral Shear Forces at Beam-Column or Slab-Column Joints. (AS 3600 Clause 10.7.4.5 and others) A calculation is required to obtain the quantity of reinforcement within the joint. A formula is provided to give the quantity of bar or mesh. The University of Sydney Page 55 The offset is located just above the lap at the "working floor level". Orientation problems of the crank are eliminated, the bar continues straight through the floor above and fitment dimensions can be made identical on each floor and through the joint itself if shear steel is needed. Cranked Column Bars above Working Floor Level The University of Sydney Page 56 The offset occurs through the beam or floor level. Unless the beam steel can be moved sideways, the cranked portion creates scheduling and fixing problems in deciding how to get beam steel through the cranked portion. Beam-column intersection problems will always be severe with narrow beams. Band beams provide a good solution. Cranked Column Bars within Band Beams The University of Sydney Page 57 Location of Column Ties within the Column Height Spacing is generally uniform but it is necessary to indicate the location of the highest and lowest ties, usually 50 mm above the floor or kicker below and 50 mm below the highest soffit above. Location of Column Ties within Column Height The University of Sydney Page 58 Concrete Stair Reinforcement Details The University of Sydney Page 59 The University of Sydney Page 60  References – Apostolos Konstantinidis “Earthquake Resistant Buildings Volume A “, Alta Grafico A.E.2015. – The University of Sydney Page 61