Inclined column is not vertical which are used in many construction works for aesthetics and architectural requirements. Inclined column design, loads and bending moment in inclined columns are discussed.
A vertical structural member subjected to axial compression in the majority with some or no moment is termed as a column. If the same member is inclined, it is a strut. But all these members in common are subjected to compression in the majority and they are categorized as strut members.
Fig.1: Inclined columns of a stadium
Fig.2: Two Precast Grand Beams Arranged that are supported by an inclined columnWhen we consider an inclined column (say strut) the forces it is subjected to are axial compression, moments and shear, which can be found out by any method of frame analysis. We have mostly seen in many of the structural analysis problems we have dealt with inclined columns. But there is no variation in the method of analysis that we perform on it. The design in most of the cases is carried out for axial force and moments by the usual method. In a condition where shear is found predominant (this is the case when the member is inclined appreciably), shear reinforcement should be designed and their provision is made. Some of the examples of inclined column constructions are rafter & struts of an RCC truss, gable beams of a sloped roof, and the top chord of an RCC Virendeel Girder. The top chord (beam) of a Virendeel girder, which is a horizontal member, is designed as a column, and not as a beam, as compression is dominant in it.
Load Transferring and Deflection
Fig.3: An Inclined Column – Load DeflectionA column that possesses a cross-section without symmetry may be subjected to torsional buckling or lateral buckling. Torsional buckling is a sudden twisting of the column. As the theories say the existence of eccentric loading would decrease in column strength. The term eccentrically loaded is defined as the situation when the axial load on the column is not concentric or in other words if the line of action of the axial load is not parallel to the central axis of the column. The eccentricity mainly represented by ‘e’, of the load subjects to bending of the column immediately. Hence the combined action of axial and bending would result in reduced load carrying ability.
Fig.4: Inclined Column Subjected to Eccentric Axial Load
Loads and Bending Moment in an Inclined ColumnFigure 5 below shows an inclined column connected a beam. We will discuss how we can determine the load in the column.
Fig.5: Inclined Column - Beam ConnectionFrom the figure the w = total load applied to the beam. This is the load that has to be transferred to the inclined column AB. The axial force P can be obtained by the equation
M = P.eWhere e is the eccentricity. From the figure, ‘e’ has to be determined from the given details. Thus,
Once the column is analyzed and the loads, forces are determined the next procedure is design of inclined column.
Design of Inclined ColumnThe inclined column design is like vertical columns
- Determine the type of column by calculating the effective length and the end conditions
- For the maximum moment, value determines the reinforcement