Type of structural joints
- 2. Group NO:7 1. Hanzlah Akhlaq 2k15-MS-PT-STR-04 2. Zahid Mahmood 2k15-MS-PT-STR-05
- 4. Introduction of Joints • Concrete is subject to change in length, plane, and volume due to changes in its temperature, moisture content, reaction with atmospheric carbon dioxide and maintenance of loads. • The effects may be permanent contractions to initial drying shrinkage, carbonation, and irreversible creep. • Other effects are transient and depend on environmental fluctuations in humidity and temperature and may result in either expansions or contractions.
- 5. Movements in Structure • The movements in hardened concrete that can cause cracking can originate from: 1. The Movements that are independent of the type of structure; these properties include shrinkage. 2. Movements depending on the type of structure and consisting of effects of all imposed loads such as self weight and lateral loads of wind and earthquakes. Such movements may be deflections, elastic strains, and strains due to creep caused by permanent loads. 3. Movements depending on the location of the structure caused by changes in temperature and humidity.
- 6. Joints Terminology • Joints will be designated by a terminology based on the following characteristics: resistance, configuration, formation, location, type of structure, and function. • Resistance: Tied or reinforced, doweled, non doweled, plain. • Configuration: Butt, lap, tongue, and groove. • Formation: Sawed, hand-formed, tooled, grooved, insert formed. • Location: Transverse, longitudinal, vertical, horizontal. • Type of Structure: Bridge, pavement, slab-on-grade building. • Function: Construction, contraction, expansion, seismic, hinge. • Example: Tied, tongue and groove, hand-tooled, longitudinal pavement construction joint.
- 7. Jointing practice Four primary methods are available for creating joints in concrete surfaces forming, tooling, sawing, and placement of joint formers. • Formed joints: These are found at construction joints in concrete slabs and walls. Tongue and groove joints can be made with preformed metal or plastic strips. • Tooled joints: Contraction joints can be tooled into a concrete surface during finishing operations. A groove intended to cause a weakened plane and to control the location of cracking should be at least 1/4 the thickness of the concrete.
- 8. Jointing practice • Sawed joints: Use of sawed joints reduces labor during the finishing process. Labor and power equipment are required within a short period of time after the concrete has hardened
- 9. Jointing practice • Joint formers: Joint formers can be placed in the fresh concrete during placing and finishing operations. Joint formers can be used to create expansion or contraction joints. Expansion joints generally have a removable cap over expansion joint material.
- 11. Construction Joints Definition: 1.Construction joints are stopping places in the process of concrete pouring. 2.Construction Joints are required because it is impractical to place concrete in a continuous operation, except for very small structures. 3.These are normally required in construction works because there is limited supply of concrete in concrete batching plants in a single day and the size of concrete pour may be too large to be concreted in one go. 4.Construction joints may run horizontally or vertically, depending on the placing sequence prescribed by the design of the structure.
- 12. Construction Joints Definition: 5. These joints are installed to break up the structure into smaller units in accordance with the production capacity of the construction site. 6. For monolithic concrete, a good construction joint might be a bonded interface that provides a watertight surface, and allows for flexural and shear continuity through the interface. Without this continuity a weakened region results that may serve as a contraction or expansion joint. 7. Correctly located and properly executed construction joints provide limits for successive concrete placements, without adversely affecting the structure.
- 13. Construction Joints Formation: The main problem in the formation of a good construction joint is that of 1. Obtaining a well-bonded watertight joint between the hardened and the fresh concrete. 1. For a sound joint, the reinforcing should be cleaned, and the aggregate of the hardened concrete should be exposed by brushing, water blasting, or sandblasting before placing the new concrete. 2. If there should be any doubt as to the adequacy of the bond between the old and new concrete, the reinforcement crossing the construction joints should be supplemented by dowels.
- 14. Types of Construction Joints Butt Joints: The simplest type of construction joint is a butt type formed by the usual bulkhead board, as in Fig 1. This joint is suitable for thin slabs. Tongue and Groove Joints : Slabs can use a type of joint that resembles tongue and groove lumber construction. The keyway may be formed by fastening metal, wood, or pre-molded key material to a wood bulkhead. Concrete above the joint should be hand tooled or saved to match a control joint in appearance. Figure 1: Butt Joint in Structural Slab
- 15. Types of Construction Joints The second placing of concrete later enters the groove to form the tongue and thus allow for shear forces to be transmitted through the joint, In plain slabs on ground this ensures that future slabs will remain level with previously cast concrete. Figure 2:Tongue and Groove joint in Slabs
- 16. Location of Construction Joint 1. Construction joints parallel to the slab span can be placed anywhere, except those locations in T-beam construction that rely on a portion of the slab to act with the beam in resisting flexure. 2. For slabs and beams it is, therefore, usual to have construction joints at mid span of the middle third of the span. (ACI 318-11, Section 6.4.4). 3. Joints in girders shall be offset a minimum distance of two times the width of intersecting beams. (ACI 318-11, Section 6.4.5). 4. Designing concrete members for lateral forces may require special design treatment of construction joints.
- 18. Location of Construction Joint 5. In walls a horizontal length of placement in excess of 40 ft is not normally recommended. 6. It is convenient to locate horizontal joints at the floor line or in line with window sills. 7. In the design of hydraulic structures, construction joints usually are spaced at shorter intervals than in non hydraulic structures to reduce shrinkage and temperature stresses. 8. If the placing of concrete is involuntarily stopped for a time longer than the initial setting time of the concrete, the old surface is to be considered as a construction joint, and treated as such before casting is resumed.
- 19. Location of Construction Joint 8. However from the point of view of strength of the structure, it is desirable to position construction joints at points of minimum shear. 9. Shear keys, diagonal dowels, or the shear transfer method (ACI Code 318-11, Section 11.7) may be used. Construction joint used as contraction joint in slab or wall
- 20. Expansion Joints
- 21. Expansion Joints Expansion joints are used to allow for expansion and contraction of concrete during the curing period and during service. These Joints are used; • To permit dimensional changes in concrete due to load. • To separate, or isolate, areas or members that could be affected by any such dimensional changes. • To allow relative movements or displacements due to expansion, contraction.
- 22. Expansion Joints • Differential foundation movement, or applied loads. • Expansion joints are frequently used to isolate walls from floors or roofs, columns from floors or cladding, pavement slabs and decks from bridge abutments or piers, and in other locations where restraint or transmission of secondary forces is not desired. • Many designers consider it good practice to place expansion joints where walls change direction as in L- T- Y-, and U-shaped structures.
- 23. Function of Expansion Joints. • Expansion joints should not be provided unless they are very necessary, since they can be an embarrassment to the structural and architectural designer, as they are often incompletely detailed and frequently badly constructed. 1. They act as stress relief planes. 2. The concrete between the joints is not subjected to substantial volume change stresses.
- 24. Function of Expansion Joints. 3. Other elements supported by the concrete, such as partitions, exterior cladding, window frames, and others in the building, are not subjected to movement distress. 4. The shape, size, and type of joint will function correctly for all conditions of movement. Factors that should be considered in the design and de tailing of expansion joints are: shrinkage, creep, thermal movements, foundation settlements, and elastic deformations of adjacent structural units.
- 25. Location of Expansion Joint 1.Many designers consider it good practice to place expansion joints where walls change direction as in L- T- Y-, and U-shaped structures, and where different cross sections develop. Figure 3 :Joints related to shapes of Building
- 26. Location of Expansion Joint 2. Expansion joints may be necessary at the junction of tall and short buildings (Fig.4) to avoid distress due to differential settlements 3. When expansion joints are required in nonrectangular structures, they should always be located at places where the plan or elevation dimensions change radically. Figure 4 :Joints related to shapes of Building
- 27. Location of Expansion Joint 4. The simplest expansion joint is one on a column line with double columns. Figure 5 :Joints related to shapes of Building
- 28. Location of Expansion Joint 5.Expansion joints without a double column may be used by introducing them in the third or quarter point in the slab as in fig 6. 6. Joints should extend through foundation walls, but column footings need not be cut at a joint unless the columns are short and rigid. No reinforcement should pass through these joints; it should terminate 2 in. from the face of the joint. Dowels with bond breaker may be used to maintain plane. Figure 6 :Joints related to shapes of Building
- 29. ACI Committee 350, 2006 Standards • ACI 350R stipulates that “in general, expansion joint spacing preferably should not be greater than 120 ft ”; however, engineering practice over the decades and effluent leakage failures have revealed that this spacing limit is too excessive. A modification of the ACI 350 standard given in Table 1 recommends joint spacing and widths, with a maximum spacing of 100 ft otherwise, wide liquid-leaking cracks could develop. It should be emphasized that the actual width of the joint should be at least twice the expected movement. Table 1 : Recommended Joint Width and spacing
- 30. Joints in Concrete Construction ACI 224.3R-95 Table 1.1 Expansion Joint Spacing
- 31. Seismic Joints
- 32. Seismic Joints • Seismic joints are wide expansion joints provide to separate portions of buildings dissimilar in mass and in stiffness. The seismic joint coverage must allow movement, and be architecturally acceptable. • The width of a seismic joint should be equal to the sum of the total deflections at the level involved from the base of the two buildings, but not less than the arbitrary rule of 1 in. for the first 20 ft of height above the ground, plus 1/2 in. for each 10 ft additional height. • The determination of these deflections will be the summation of the story drift in addition to the building's flexural deflection to the level involved. Shear wall buildings, being much stiffer, need a seismic joint only ,say, half as wide, since the earthquake oscillations of shear wall buildings will be much smaller than those of framed buildings.
- 33. Seismic Joints (a) Roof parapet separation. (b) Plan at exterior vertical closure. Seismic separation joint details
- 34. Seismic Joints • Nonsymmetrical configuration with reentrant corners (e.g., L-or H- shaped buildings) are particularly susceptible to destructive torsional effects. Primary damage often occurs at the reentrant corners. • Allowing separate building masses to vibrate independently by using seismic separator joints that allow free movement to occur generally improves structural performance.
- 37. Details and Detailing of Concrete Reinforcement (ACI 315-99)
- 41. Contraction Joints • A contraction joint is formed by creating a plane of weakness. Some, or all, of the reinforcement may be terminated on either side of the plane. Some contraction joints, termed “partial contraction joints,” allow a portion of the steel to pass through the joint. These joints, however, are used primarily in water-retaining structures. • Contraction joints consist of a region with a reduced concrete cross section and reduced reinforcement. The concrete cross section should be reduced by a minimum of 25 percent to ensure that the section is weak enough for a crack to form
- 42. Contraction Joints • In terms of reinforcement, there are two types of contraction joints 1. Full contraction joints (ACI 350R). 2. Partial contraction joints (ACI 350R). • Full contraction joints: Full Contraction joints are constructed with a complete break in reinforcement at the joint. Reinforcement is stopped about 2 in. from the joint and a bond breaker placed between successive placements at construction joints. • Partial contraction joints: A portion of the reinforcement passes through the joint in partial contraction joints. Partial contraction joints are also used in liquid containment structures.
- 43. Contraction Joints • Water stoppers can be used to ensure water tightness in full and partial contraction. • Contraction and expansion joints within a structure should pass through the entire structure in one plane. If the joints are not aligned, movement at a joint may induce cracking in an un-jointed portion of the structure until the crack intercepts another joint.
- 44. Location of Contraction Joints • Table 1.1 shows recommendations for contraction joint spacing. • Recommended spacing's vary from 15 to 30 ft (4.6 to 9.2 m) and from one to three times the wall height. • The Portland Cement Association (1982) recommends that contraction joints be placed at openings in walls, as illustrated in Fig. 3.1. Sometimes this may not be possible.
- 46. Location of Contraction Joint