Supplemental structural members are additional columns, beams, braces, and walls that are built to provide support to weakened structures. This technique aims to either restore the original strength of a deteriorated structure or enhance its capacity to bear heavier loads under various environmental conditions. The method of adding supplemental structural elements is commonly employed in the rehabilitation of structures that have suffered damage from earthquakes. By doing so, the load-carrying ability, stiffness, and ductility of the structure can be regained, thereby strengthening it.
When Supplemental Structural Members are Required?
There is a repair method that can be used when none of the other strengthening techniques are effective. This method not only helps to repair deteriorated buildings but can also be employed to increase the lifespan of structures, particularly bridge structures. This technique is specifically suitable for strengthening buildings that have been impacted by earthquakes.
In situations where deficiencies exist in the global strength, global stiffness, configuration, the span of diaphragms, and lateral ductility of the overall structural system, new shear walls, braced frames, or moment frames can be added to an existing building. These additions can mitigate the aforementioned deficiencies, thereby improving the overall structural system’s strength and performance.
By employing this technique, structures can be reinforced to withstand the impacts of earthquakes, which are often unpredictable and can cause extensive damage. Additionally, this repair method can help to extend the lifespan of structures, which is essential in ensuring the safety of the occupants and the general public who rely on these structures for transportation, housing, and commerce.
Purpose of Supplemental Members
Supplemental members refer to additional structural elements such as columns, beams, braces, or infilled walls that are installed to provide support for damaged or compromised members. The purpose of these elements is to stabilize the structural framing by positioning them below the damaged or deflected areas. The installation of new members is a cost-effective technique that is commonly used to support severely cracked and deflected flexural members.
To ensure the structural integrity of the building, it is necessary to incorporate cross bracing, infilled walls, or other methods of resistance to lateral forces if the original structure has lost its ability to resist such forces. The use of supplemental members is a rapid installation process that makes them an ideal solution for temporary emergency repairs.
Supplemental members can be installed quickly and effectively, making them an optimal choice for stabilizing the structure during emergency repairs. They are designed to provide support and stability to damaged structural elements and are typically positioned below the damaged or deflected areas. Furthermore, the use of supplemental members is a cost-effective technique for supporting severely compromised flexural members. If the original structure has lost its ability to resist lateral forces, it is necessary to incorporate cross bracing, infilled walls, or other forms of resistance to ensure the structural integrity of the building.
Factors Considered for Supplementing Damaged Concrete Structures?
The installation of new columns can impede passage through a space, while the addition of new beams can decrease the available headroom. Furthermore, these new structural elements can be visually unappealing and detract from the overall aesthetic of the design.
Infilling walls or incorporating cross bracing can also negatively impact the effective use of interior space. Additionally, it is important to consider the potential effects of the supplemental members on the existing structure, as they may not fully relieve loads and stresses without special measures.
Furthermore, the introduction of new structural members can result in a redistribution of loads and forces that could potentially over-stress nearby members, as well as the foundation.
It is also important to note that a simply supported beam propped by a column at its midpoint will not behave in the same manner as a two-span continuous beam. As such, any expected cracking at the top of the central support must be carefully investigated and accounted for in the design process.
Installation of Supplemental Structural Members
The new members, which can be made of timber, steel, concrete, or masonry, are carefully installed by shimming, wedging, or anchoring them in position to transfer loads. It is important to ensure that the packing force used is not too large, as it could cause lifting of repaired and adjoining members beyond their original position and result in stress reversal. In cases where a beam supported on columns has shear cracks, adding a post adjacent to an existing column can improve shear resistance and reduce the effective span of the beam, potentially providing a more economical solution than collars. The eccentric positioning of the post over an existing footing needs to be analyzed to determine if it is sized and strengthened adequately. Jacking may be required before installing the props to effectively redistribute dead loads to the new posts. In some instances, a full new frame may be fitted within the existing frame by erecting two columns adjacent to the existing columns and constructing a new beam below the existing beam. The space between the new beam and existing structure can be shimmed or dry-packed. To provide lateral stability to the supplemental member, it may be necessary to mechanically anchor it to the existing slab, columns, or both. Extra beams may also be provided on top of the existing beams to strengthen an existing slab.
Fig. 4: Addition of Reinforced Concrete Shear Walls