What are Stirrups?
Stirrups are light metal frames suspended from the saddle attached to the horse or pony back. It provides the necessary support to the rider’s feet while riding and helps during mounting the horse. Stirrups were invented around the 2nd Century BC that increased the combat value of the horse. When the device reached Western Europe in the 8th Century, it was coupled with lance and shield to envisage a new kind of horsemanship; the mounted knight. The stirrups horse helps the rider to maintain balance while riding and uphold his seat during a moment of impact.
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There are many types of stirrups when one thinks of English stirrups; mostly, the vision of Fillis stirrups comes to mind. This sort of stirrups is a retro, traditional type with no decoration. The standard stirrups weigh less than Fillis one, as the latter weighs more at the bottom, making it the preferred stirrups for most riders.
Types of Horse Stirrups
Offset and offset eyes are other types of stirrups; in the first one, the eye of the stirrup leather is diagonal rather than straight in the center. The design is crafted to maintain a proper comfortable leg position. On the contrary, in offset eye stirrup, the eye is twisted to prevent distortion of stirrup leather and also support leg arrangement. Other types of stirrups are safety stirrups, one side is crafted from stainless steel like regular, but the other is made of resilient rubber. The rubber will snap if a rider falls, averting further injury.
Two Meanings of Stirrups
Stirrups meaning is both a pair of light metal frames or ring to support the foot of a rider, fastened by a band to the saddle and helps in mounting and dismounting. In construction, a stirrup's meaning is an enclosed steel ring that supplements extra reinforcement to beams and bars, preventing deformation or crumple under the brick and mortar weight.
The main purposes of stirrups in construction are as follows:
It enhances the comprehensive strength of beams and columns.
It improves the ductility of the structure.
It supports the main reinforcement in columns and prevents distortion.
During concreting, it prevents movement of main reinforcement.
It gives cross detention to longitudinal bars.
It provides resistance against torsion and shear.
It clasps longitudinal bars during construction.
It restricts the concrete in the core improving ductility and strength of the structure.
Stirrups in the beam upholds the main reinforcement of the beam. Stirrups are imposed at regular intervals in beams and columns to prevent collapse. Also, they act as a shock absorber, protecting the RCC structure during seismic activities. Different types of stirrup are used in construction; one, two, three, four, five, six, and seven-legged. One-legged and 2 legged stirrups are used in the lower dimension of beams and columns, while three to seven-legged stirrups are used in higher dimensions. 2 legged stirrups are used in lower dimensions having less girth than respective depth.
Different types of the stirrups in columns are designed depending on their various cross-sections, the number of longitudinal reinforcement bars, and their load-carrying capacity. Stirrups used in columns are known as vertical ties or transverse reinforcement. The main purpose of the stirrup is to hold primary reinforcement columns in place; the minimum distance of vertical stirrups should be 100mm per c/c throughout the length.
Shear Stress
When an external force is exerted on an object, it undergoes deformation. If the exerted force is parallel to the plane of the object, the buckle will be along the plane. The stress the object experiences is shear stress or tangential stress. The cause of shear stress is shear force, a couple of forces acting with the same magnitude on the opposite side of the body. In the realm of construction, shear can mean different things. The shear stress can occur in the structural member due to applied load. It can also be referred to as lateral load arising out of wind or earthquake. Shear stirrup reinforcement is used at a suitable spacing to negate the shear stress.
There are three types of shear reinforcement; vertical stirrups, bend bars along with stirrups, and inclined stirrups. These reinforcements are designed to negate shear forces in excess of to shear strength of concrete. Due to simplicity in fabrication and installation, stirrups are mostly used as shear reinforcement. More stirrups are placed in the high shear region with more ductility and reinforcement though it increases the time and cost of installation.
Thus, the article has included all the important information regarding stirrups to help you understand the topic better.
FAQs on Stirrups
Q.1 Why are stirrups in beams and columns?
Stirrups are placed at stipulated intervals in beans to prevent buckle and shear failure. Steel rebar is tensile than stirrups, often installed with rebar. Rebar acts as bones to the structure. The stirrups reinforce them upholding their strength and straightness. The stirrups inside the concrete columns enhance their durability. Stirrups are installed vertically and diagonally, and it is done to prevent shear failure as cracks in beams mostly occur diagonally. Transverse steel tie bars are used to hold the main bars in position. The stirrups provide protection to the RCC structure during seismic activities. Stirrups hold the longitudinal bars in position and prevent the busting of lateral reinforcement into concrete.
Q.2 How do stirrups prevent earthquake damage?
In RC structures, vertical, horizontal structures (columns and beams) are integrally attached. The load is transferred from one to another, as the members act as a frame. Beams are installed with two reinforcements; one is long straight bars (longitudinal bars) placed horizontally, other is a closed loop or ring (stirrups) placed vertically at regular intervals. To prevent damage from moderate to severe earthquakes, the installed stirrups must be 6mm, and for beams more than 5 meters, it should be 8mm. Both ends of the vertical stirrups must be inserted into a 135-degree hook and extended adequately to prevent opening up in seismic activity. If the length of the beam is double its respective depth, the placing of stirrups must be more stringent.
Q.3 How are column ties different from beam stirrups?
Though both appear to be the same but differ in their projected function, ties are used as transverse reinforcement in columns where the prime mode of load transport is compression. Primarily ties are installed to prevent premature buckling of bars and to restrict concrete in the core. While stirrups are transverse reinforcement placed on beams and the mode of load transfer is via bending and shear. The main objective of this reinforcement is to avert shear cracks in the beams which could lead to failure. Stirrups provide additional shear strength to concede and are crafted accordingly. Both steel and concrete act jointly in resisting shear force.