Earthquake-Resilient Foundation Design

How Do Structures Transfer Their Base Shear to Soil, and Why Is It Crucial? Understanding how lateral loads move through a structure and into the soil is a basic but often overlooked part of structural engineering. This knowledge is essential for checking an important assumption in our structural analysis: the fixed base model. This approach simplifies structural analysis by assuming that there is no movement at the soil level, which makes calculations easier. However, this can lead to significant discrepancies between analytical predictions and the actual behaviour of structures. This assumption is no longer the most efficient approach and may not be safe either. Mechanisms of Lateral Load Transfer to Soil: Many engineers are familiar with vertical foundation movements related to uplift forces and soil bearing capacity. However, the lateral movements of the foundation and their effects on structures are less frequently discussed. Here is a brief description of the mechanisms through which foundations transfer lateral loads to the soil: • Friction: This is the resistance that occurs as the foundation moves relative to the soil. • Passive Resistance: Lateral forces push the foundation against the soil through elements like ground beams and engage the soil to provide resistance (via minor axis bending of beams). • Piles: These function by pushing against the soil, utilizing a mechanism similar to passive resistance described above. Slab on Grade as a Transfer Floor: In scenarios where these mechanisms under lateral resisting elements are inadequate, how well the foundation system is connected becomes vital. This is particularly true if there are missing tie beams or insufficient reinforcement in the slab on grade. Recognizing the slab on grade as a crucial “transfer floor” is essential for addressing these issues. Here are strategies to enhance foundation design and performance: • Reinforcement: A diaphragm analysis of the slab on grade is crucial. It should include reinforcement details similar to those in suspended floors, often determined through methods like grillage analysis (refer to Section 5 - Appendix C5D of the NZ seismic assessment guidelines). • Tie Beams: These are essential for providing both passive resistance and functioning as diaphragm ties, facilitating load transfer across the foundation. • Ductile Reinforcement: Using ductile reinforcement in the slab is essential to maintain tensile capacity and manage large strains. • Connections: Strong connections between the slab on grade, lateral resisting elements, and footings are crucial for effective load transfer. By designing the foundation floor to function effectively as a diaphragm, we significantly enhance the building's efficiency and resiliency to withstand lateral forces. Keep an eye out for a future post, where I will discuss soil-structure interaction modelling and lateral assessment of piles. #structuralengineering #earthquakeengineering #seismicdesign #resilience

Base isolation refers to a technique used in structural engineering to protect buildings and other structures from the potentially damaging effects of ground vibrations during earthquakes or other dynamic events. It involves the installation of flexible or resilient materials between the foundation (base) of the structure and the ground, effectively decoupling the superstructure from the ground motion. Common materials used for base isolation include rubber bearings, laminated elastomeric bearings, or friction pendulum bearings. Base isolators are special engineering devices used in earthquake zones to protect buildings from damage during earthquakes. They essentially act as shock absorbers for structures, isolating them from the shaking ground. There are two main types of base isolators: 1.Elastomeric bearings: These are the most common type and are made of thick layers of rubber vulcanized between steel plates. They function by deflecting horizontally during an earthquake, lengthening the building’s vibration period and reducing the forces transmitted to it. 2.Friction pendulum bearings (FPBs): These isolators use a curved sliding surface and a pendulum effect to create a restoring force and dissipate energy through friction. Main dynamic effects of base isolation on the super structure includes: (1) increasing the natural period of the structure (2) decreasing acceleration responses, as well as inter-story displacements. #concretedesign #steelstructures #concrete #civilengineering #structuralengineering #structure #steel #construction #arhitecture #civil #civilengineer #civilconstruction #engineering #engineer #inovation #engineeringstudent #engineeringstudents #dynamics #structuralanalysis #Resilience #Building #DisasterMitigation #Engineering #Innovation #baseisolators #Technology #Design

𝗕𝘂𝗶𝗹𝗱𝗶𝗻𝗴 𝗥𝗲𝘀𝗶𝗹𝗶𝗲𝗻𝗰𝗲 𝘄𝗶𝘁𝗵 𝗘𝗮𝗿𝘁𝗵𝗾𝘂𝗮𝗸𝗲 𝗜𝘀𝗼𝗹𝗮𝘁𝗼𝗿𝘀: 𝗛𝗼𝘄 𝗧𝗵𝗲𝘆 𝗪𝗼𝗿𝗸 𝗮𝗻𝗱 𝗔𝗿𝗲 𝗜𝗻𝘀𝘁𝗮𝗹𝗹𝗲𝗱 In seismic design, base isolation has emerged as a powerful technique to protect structures from the destructive forces of earthquakes. This video illustrates how earthquake isolators are transforming engineering practices by adding a layer of resilience to modern buildings. 𝗛𝗼𝘄 𝗜𝘁 𝗪𝗼𝗿𝗸𝘀: Base isolators are installed between a building's foundation and its superstructure. They function by decoupling the structure from ground movement, allowing controlled lateral motion. By reducing the transfer of seismic energy, these isolators significantly lower the risk of structural damage during an earthquake. 𝗜𝗻𝘀𝘁𝗮𝗹𝗹𝗮𝘁𝗶𝗼𝗻: The process involves placing flexible, energy-absorbing pads—often made of steel, rubber, and lead—at key points between the building’s foundation and the floors above. These isolators effectively absorb and dissipate seismic forces, ensuring that the main structure remains stable. 𝗪𝗵𝘆 𝗜𝘁 𝗠𝗮𝘁𝘁𝗲𝗿𝘀: Base isolation not only enhances a building’s ability to withstand seismic forces but also reduces repair costs and downtime after an event. As engineers, implementing these innovations is a critical step towards creating safer, more resilient cities. #SeismicEngineering #BaseIsolation #ResilientDesign #StructuralEngineering #CivilEngineering #InfrastructureSafety