Lecture 3 Elements of Skeleton System PDF

Mousl university2nd semester : Building Construction Architecture department2 Date : xx / xx / xxxx Elements of skeleton system 1. Column Building Construction 2...

Mousl university2nd semester : Building Construction Architecture department2 Date : xx / xx / xxxx Elements of skeleton system 1. Column Building Construction 2 Assistant Teacher. : Adil Khalil Column Column is a vertical member which takes complete load of the beam, slabs and the entire structure and the floor and other area of the building is adjusted as per the requirement of the client or owner. The size of the columns, quantity of cement sand and aggregate to be mixed, the number of steel bars to be placed, spacing between the stirrups is all mentioned in the structural drawing which is designed by structural designer as per the actual load on the column and considering the factor of safety. A column is a vertical member which effectively takes load by compression. Basically column is a compression member as load acts along its longitudinal axis. Bending moment may occur due to wind earthquake or accidental loads. Column transfers the load of the structure of slabs beams above to below, and finally load is transferred to the soil. Columns location should be such that it hides in the walls partially or fully. Construction Methods of RCC Columns Construction of RCC columns involve following four steps: A. Column layouts ‫الشبكة االنشائية‬ B. Column reinforcement work ‫تسليح االعمدة‬ C. Column formwork‫شد القلب الخشبي او المعدني‬D. Pouring of concrete ‫عملية صب الخرسانة‬ A. Layout of Columns Column layouts are done by laying rope in the grid lines and mark the location of columns. B. Column Reinforcement ‫تسليح االعمدة‬ Column reinforcement works needs following checklist on site: Check the numbers and diameter of vertical bars Spacing between vertical bars Lapping in alternate bars should come at same height. ‫العمود المكمل يكون بنفس االرتفاع‬ Lapping should not come inside beam or slab. Lapping should be at l/3 or 2/3 of column as per structural notes Spacing between stirrups is as per the drawing Hook should be bend properly at right angles. Check the stirrups corner. Vertical bar should come at right angle edge of stirrup properly bound with binding wire ‫يجب ان يكون شيش التسليح مع‬ ‫الزاوية القائمة للحلقة‬ C. Column Formwork Columns carry the load of structure and hence they are critical. It is important to align them for verticality so that load is transmitted properly. ‫يجب التأكد من شاقوية االعمدة لتنقل االحمال بشكل صحيح‬ The column shuttering should be strong enough to take the pressure of fresh concrete and remain in position during concreting. ‫يجب اغالق االعمدة بشكل محكم لتحنل الضغط والزحف‬  Some Guidelines on column shuttering To hold the concrete shuttering firmly in place and for proper alignment a concrete pad called starter is cast before fixing the shuttering. ‫عمل مقدمات االعمدة كيكرز‬ The thickness is about 45 mm to 60 mm and dimensions are precisely the same as the dimensions of proposed column. ‫ نفس موقع وابعاد العمود‬60-45 ‫سمك‬ The starter should be cured for a day or 2 so that it is hard enough to fix the shuttering around it. Column box or shuttering for columns is made of plywood sheets or steel sheets fabricated with adequate stiffeners. A thin films of oil or grease should be applied to inner surface of the shuttering to enable easy removal of the column after the concrete hardens. Shuttering should be properly aligned to its verticality and diagonals to be checked to ensure accuracy in dimensions..‫يجب ان تكون المحاذاة متوافقة بشكل صحيح مع خطيها وأقطارها للتأكد من الدقة في األبعاد‬ Formwork has to be thoroughly supported with props size before pouring the concrete so that it does not moves horizontally or vertically during concreting. ‫تثبيت قوالب الخرسانة بشكل كامل قبل صب الخرسانة بحيث ال تتحرك أفقيا ً أو رأسيا ً أثناء عملية‬ ‫الصب‬The gaps near the shuttered joints should be sealed with plaster or a piece of wood to prevent any leakage of slurry. ‫اية ثغرات تغلق بالجص‬ It is preferable to remove shutters after 24 hrs. of casting and if they need to be removed earlier, it should not be removed within sixteen hours. The removal of shutters has to be done gently without jerks so that edges of columns are not damaged. ‫الحذر عند فتح الفخخ لعدم ضرر الحافات‬ Care should be taken regarding fixing and supports of column shuttering to prevent it from movement during concreting. ‫التأكد من احكام غلق االعمدة‬ Diagonals of the shuttering to be checked to ensure dimensional accuracy. ‫فحص األقطار للتأكد من دقة االبعاد‬ D. Concreting of RCC Column Concreting of an RCC column can be done Manually With the help of machine or pump Manual Concreting of RCC Column Concreting of RCC Column using Pump Following points to be followed during and after concreting: For less quantity machine mix concrete is done and for larger quantity ready mix concrete (RMC) is ordered.‫التأكيد على استخدام خرسانة جاهزة‬ Approval of placing concrete whether by pump or manually has to be taken from client. ‫الخرسانة اليدوية بموافقة الجهة المستفيدة‬ Concrete should be poured up to slab bottom; the remaining column gets concreted during pouring of slab & beam. ‫التأكد من وصول الخرسانة الى اسف العمود‬ Mechanical vibrator to be compulsorily used in the column but excess vibration can cause segregation. Each layer should be thoroughly compacted. Target slump to be 160 mm. ‫ سم‬160 ‫استخدام الهزاز كل‬ Height of pouring concrete should not exceed 1.5 m. Construction joint should be avoided in the column. Temperature should be below 30 degree while pouring concrete. After the pouring of concrete and vibrating it with the help of a vibrator the horizontality and verticality of column to be checked  Types of columns There are several types of columns which are used in different parts of structures. Column is a vertical structural member that carry loads mainly in compression. It might transfer loads from a ceiling, floor slab, roof slab, or from a beam, to a floor or foundations. Commonly, columns also carry bending moments about one or both of the cross-section axes. In this article, different types of columns used in building construction will be discussed. Types of Columns in Building Construction Columns are classified based on the several conditions which include: 1. Based on Types of Reinforcement.1 2. Based on Types of Loading.2 3. Based on Slenderness Ratio3.3 4. Based on Shape.4 5. Based on Construction Material.5 1. Based on Types of Reinforcement 1. Tied Column This type of column is commonly construction from reinforced concrete. Longitudinal reinforcement are confined within closely spaced tie reinforcement. It is estimated that 95% of all columns in buildings are tied.  3. Composite column When the longitudinal reinforcement is in the form of structural steel section or pipe with or without longitudinal bars, it is called as a composite column. This type of column have high strength with fairly small cross section, in addition to exhibit good fire performance. 2. Based on Types of Loading 4. Axially Loaded Column If vertical axial loads act on the center of gravity of the cross-section of the column, then it is termed as axially loaded column. Axially loaded column is rare in construction since coinciding vertical loads on the center of gravity of column cross section is not practical. Interior column of multi-storey buildings with symmetrical loads from floor slabs from all sides is an example of this type of column. 5. Column with Uniaxial Eccentric Loading When vertical loads do not coincide with center of gravity of column cross section, but rather act eccentrically either on X or Y axis of the column cross section, then it is called uniaxially eccentric loading column. Column with uniaxial loading are generally encountered in the case of columns rigidly connected beam from one side only such as edge columns. 6. Column with Biaxial Eccentric Loading When vertical on the column is not coincide with center of gravity of column cross section and does not act on either axis (X and Y axis), then the column is called biaxially eccentric loaded column. Columns with biaxial loading is common in corner columns with beams rigidly connected at right angles at the top of columns. Biaxial column: Designed for axial load and moment in 2 directions  3. Based on Slenderness Ratio Based on slenderness ratio, (effective length/ least lateral dimension), columns are categorized as follow: 6. Short Column If the ratio effective length of the column to the least lateral dimension is less than 12, the column is called as the short column. A short column fails by crushing (pure compression failure). 7. Long Column If the ratio effective length of the column to the least lateral dimension exceeds 12, it is called as long column. A long column fails by bending or buckling. 4. Based on Shape Shape of Reinforced Concrete Column 8. Square or Rectangular Column They are generally used in the construction of buildings. It is much easier to construct and cast rectangular or square columns than circular ones because of ease of  shuttering and to support it from collapsing due to pressure while the concrete is still in flowable form. 9. Circular column They are specially designed columns, which are mostly used in piling and elevation of the buildings. 10. L-Shape Column Commonly, L-shaped column is utilized in the corners of the boundary wall and has similar characteristics of a rectangular or square column. 1. T-Shape column It is utilized based on design requirements of a structure. T-Shaped column is widely used in the construction of bridges. 12. Shape of Steel Column There are different standard and built up shape of steel columns which are shown in Fig. and Fig. Common shapes of steel columns include I, channel, equal angle, and T-shape. 13. Shape of Composite Column The usual shape of composite columns are shown in Fig. 5. Based of column according constriction materials 14. Reinforced Concrete, Steel, timber, Brick, Block, and Stone Column.