As structural engineers, we make a difference in peoples’ lives every day as we help to ensure society’s health, safety, and welfare. This past year, many structural engineers took this responsibility to another level in the aftermath of Hurricanes Harvey (in Texas) and Irma (in Florida).
Structural engineers took a leadership role as 2nd Responders to these natural disasters through the Structural Engineers Emergency Response (SEER) Program. Structural engineers performed damage and safety assessments of communities devastated by the hurricanes to determine whether structures were suitable for re-habitation.
At the state level, SEER Committees, as part of their State Structural Engineers Association (SEA), work to recruit and educate members to become 2nd responders. At the national level, NCSEA and its SEER Committee work to establish relationships with allied organizations to support its SEA SEER Committees by focusing on the following four issues:
- SEER Committees facilitate and deliver requisite training to SEA members so they can be certified as 2nd responders. This training is offered online through the NCSEA CalOES Structural Assessment Course or FEMA’s National Incident Management System and in person through the International Code Council (ICC) Disaster Response Inspector Course.
- Roster Management consists of compiling and maintaining the comprehensive national database of trained 2nd responders through the SEER 2nd Responder Roster at www.ncsea-seer.com. This roster is a fully interactive database that can be updated as needed by the participant and searched by SEER Committee Members to obtain a listing of participants by certification and location.
- Assistance Coordination consists of coordinating and providing 2nd responder assistance to authorities having jurisdiction (AHJs) or other stakeholders. This assistance ranges from providing lists of properly trained individuals to providing coordination and logistical assistance when needed.
- SEER Committees provide advocacy by educating AHJs, allied associations, the public, and engineers on the benefits of having structural engineers participate in 2nd response.
In support of these four initiatives, NCSEA and the ICC signed an agreement at the end of 2017 to join forces on the 2nd Responder Roster to create a single database between the two organizations of volunteers willing and able to serve when disasters strike.
Once a disaster strikes, it may be too late to volunteer. As 2nd Responders, structural engineers can continue to make a difference and ensure the health, safety, and welfare of society.
The objective of cranked bars is to provide reinforcements at the bottom in the central point and reinforcements at the top adjacent to the edges both employing the same bars.
Beams generally have maximum sagging bending moment at mid span and maximum hogging moment at supports. Hence the area of bottom reinforcement bars is maximum at mid span and reduces towards supports. To resist the hogging moment at supports, maximum steel is required at top at supports.
To gain economic advantages, part of the bottom reinforcement bars is compressed at a specific distance from the support.
Usually, cranked bars are bent up at 45 degrees. These bars also facilitate to withstand shear force, in the bent up portion. Shear force becomes extreme at supports and here optimal shear resistance is necessary.
Benefits of providing crank bars in slabs
1.To withstand Hogging (Negative Bending Moment) at supports.
2.To get rid of the risk of the failure of the slabs.
3.To experience the shear force. The shear force is always larger at the sections of supports.
4.The strength of slab is raised significantly with crank bars.v
Nodal moment can be applied on the node only, while concentrated moment can be applied directly on the member without inserting a node at that location.