Download cve 503: structural engineering i - abuad lms

CVE 503: STRUCTURAL ENGINEERING I
ASSIGNMENT 1
OBOT, OFONIME GABRIEL
12/ENG03/034
To be submitted to
ENGR. JOHN WASIU
THE DEPARTMENT OF CIVIL ENGINEERING,
AFE BABALOLA
UNIVERSITY, ADO- EKITI, EKITI STATE
IN PARTIAL FULFILMENT OF
THE REQUIREMENT FOR THE AWARD OF
BACHELOR OF ENGINEERING (B.Eng.) DEGREE IN
CIVIL ENGINEERING
November 13, 2016
Question 1: Define structural dynamics.
Structural analysis is mainly concerned with finding out the behavior of a physical
structure when subjected to force. This action can be in the form of load due to the
weight of things such as people, furniture, wind, snow, etc. or some other kind of
excitation such as an earthquake, shaking of the ground due to a blast nearby, etc. In
essence all these loads are dynamic, including the self-weight of the structure
because at some point in time these loads were not there. The distinction is made
between the dynamic and the static analysis on the basis of whether the applied
action has enough acceleration in comparison to the structure's natural frequency. If
a load is applied sufficiently slowly, the inertia forces (Newton's first law of motion)
can be ignored and the analysis can be simplified as static analysis.
Structural dynamics, therefore, is a type of structural analysis which covers the
behavior of
structures subjected to dynamic (actions having high acceleration) loading. Dynamic
loads include people, wind, waves, traffic, earthquakes, and blasts. Any structure
can be subjected to dynamic loading. Dynamic analysis can be used to find dynamic
displacements, time history, and modal analysis.
A dynamic analysis is also related to the inertia forces developed by a structure when
it is excited by means of dynamic loads applied suddenly (e.g., wind blasts,
explosion, earthquake).
A static load is one which varies very slowly. A dynamic load is one which changes
with time fairly quickly in comparison to the structure's natural frequency. If it
changes slowly, the structure's response may be determined with static analysis, but
if it varies quickly (relative to the structure's ability to respond), the response must
be determined with a dynamic analysis.
Dynamic analysis for simple structures can be carried out manually, but for complex
structures
finite element analysis can be used to calculate the mode shapes and frequencies.
Question 2
State the applications/importance of structural dynamics in engineering designs
Applications of structural dynamics in engineering designs includes;
1. Fundamentals of structural dynamics and the measurement of dynamic properties.
2. Computation for the dynamic response behaviour of a simple structural system.
3. Nature of dynamic actions and structural responses including responses to an
earthquake.
4. Use of static analysis to approximate the dynamic response behaviour of a
building.
5. Calculation of dynamic forces in a building for given dynamic properties.
Question 3: Differentiate with examples forced and free vibration.
Free vibrations are oscillations where the total energy stays the same over time.
This means that the amplitude of the vibration stays the same. This is a theoretical
idea because in real systems the energy is dissipated to the surroundings over time
and the amplitude decays away to zero, this dissipation of energy is called damping.
Free vibration occurs when a mechanical system is set in motion with an initial input
and allowed to vibrate freely. Examples of this type of vibration are pulling a child
back on a swing and letting go, or hitting a tuning fork and letting it ring. The
mechanical system vibrates at one or more of its natural frequencies and damps down
to motionlessness.
Forced vibrations occur when the object is forced to vibrate at a particular
frequency by a periodic input of force. Forced vibration is when a time-varying
disturbance (load, displacement or velocity) is applied to a mechanical system. The
disturbance can be a periodic and steady-state input, a transient input, or a random
input. The periodic input can be a harmonic or a non-harmonic disturbance.
Examples of these types of vibration include a washing machine shaking due to an
imbalance, transportation vibration caused by an engine or uneven road, or the
vibration of a building during an earthquake. For linear systems, the frequency of
the steady-state vibration response resulting from the application of a periodic,
harmonic input is equal to the frequency of the applied force or motion, with the
response magnitude being dependent on the actual mechanical system. Objects
which are free to vibrate will have one or more natural frequency at which they
vibrate. If an object is being forced to vibrate at its natural frequency, resonance
will occur and you will observe large amplitude vibrations. The resonant frequency
is fo.