We start this section with an overview of earthquake ground motion. Our focus in this course will very much be on the mechanical behaviour of our dynamic models but it will serve us well to get a brief overview of some of the basics around earthquake measurement and damage quantification.

In the next lecture, we’ll start our study of mechanical behaviour. We’ll do this in the more familiar context of SDoF systems and reserve the discussion of MDoF systems for the next section. As we’ll see later in the course, the study of SDoF systems has particular relevance when we consider modal superposition - so focusing on SDoF systems here, in a course on MDoF systems does actually make sense.

We’ll start by modelling the influence of a harmonic support motion on a SDoF structure. This will allow us to determine an equation for the response of the system as a function of the support motion characteristics. This is our first foray into ground motion modelling.

We’ll build on this in the next lecture and introduce the concept of transmissibility. This will allow us to better understand how support motion propagates into the main SDoF system and how this propagation is influenced by the system’s damping and the frequency ratio between support motion and the system natural frequency.

When simulating ground-induced structural vibration, it’s convenient to compute the structural motion relative to the moving ground. After all, it’s this relative motion that induces additional stresses within the structure. We’ll consider this alternative reference frame in the next lecture.

Next, we’ll determine the relative structural response of our SDoF system subject to harmonic ground motion and then the El Centro ground acceleration record. This will require us to move away from analytical solutions and implement a numerical solution to the equation of motion.

In the penultimate lecture in this section, we’ll cover some housekeeping issues and show you how to numerically integrate acceleration records to obtain the associated velocity and displacement records - this is a helpful technique to deploy when you want to identify ground displacement and only have an acceleration record to work with.

In the final lecture in this section, we’ll briefly review response spectra. If you’re involved in seismic design, you will definitely come across response spectra so it makes sense to introduce them before we finish this section.