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Behaviour of Long Run Metal Claddings under Static and Cyclic Wind Loading…
Behaviour of Long Run Metal Claddings under Static and Cyclic Wind Loading
Investigating Pull-through Failure Behaviour of Crest-fixed Cold-formed Steel
Material
- cold-formed steel is very soft. Thus, it has high deformation rate.
Loading
- loading causes failure like cracks in the claddings. However, continuous loading will increase the diameter of the cracks, and eventually causes leakage in a building.
Span
- intermediate span should be
bigger
than end span. End span is where maximum damage occurs.
Tensile Test
Tensile test is done to identify the characteristics of a steel sample like:
Maximum elongation
Maximum loading capacity
Young's Modulus
From these, the optimum span can be obtained.
Ultimate Limit State (ULS) and Serviceability Limit State (SLS) testings
Objectives
To obtain various displacements when loading is maximum
To identify the allowable maximum displacement of the claddings
To design the claddings based on maximum displacement, and not based on its ultimate failure
Loading Procedure
The differences between static (uplift) and cyclic wind loadings are:
Uplift loadings
one direction only (upwards along the
z-axis).
maximum loading occurs here.
Cyclic loadings
two directions (back and forth horizontally along the x- and y-axis).
yield minimum loading in both directions.
This procedure is done according to the standards/guidelines.
The loadings in x, y, and z directions cause fracture failures in claddings.
The types of failures due to static (uplift) and cyclic wind loadings are:
Uplift loadings
Dimpling -> Transverse splitting -> Complete transverse splitting
Cyclic loadings
Dimpling -> Transverse splitting -> Cracking (T-type, Star-type, O-type - depending on the pressure and load ratio (R))
Introduction
Types of Claddings
Lightweight Roof Claddings
For countries with high seismic
Unsuitable for places with high winds
Heavy Roof Claddings
Example: Concrete tiles
Profile shapes
Corrugated
Trapezoidal
The claddings are fixed to the purlins with screws through the crests so that they will resist static (uplift) and cyclic wind loadings.
Improper screwing techniques will lead to failure of the claddings:
Fracture
, due to over screwing.
Cracks
, due to no washer between the crest and the screw. Often happens on the ribs of the claddings.
Numerical Simulation
Numerical simulation is using software to model the experiment.
Objectives
:
To model in various sizes and scales.
To compare the simulation data to experimental data.
To reduce cost, as doing a real life experiment in the sample's full width is expensive.
Machine Learning Application
To train the tools and algorithm in the software to predict the outcomes when the modelled sample is exposed to real-life loads like forces.
First is to train the tools and algorithm, then validate the data by comparing them to experimental values. Often the values will not be the same, but the very close to each other. This is due to uncertainties and errors.
Comparison with Existing Design Formula - testing the equations and introducing new coefficients when necessary
Design Recommendations - establishing design equations
Procedure of the experiments
Timber purlins are placed in the pressure box in certain displacements.
Metal claddings are screwed on top of the purlins.
A pressure loading actuator pumps out air/wind into the pressure box. Another hose sucks the wind to create fluctuations of pressure in the box.
Pressure is increased until the screws fail. Then the data is recorded.
The experiment is repeated by changing the metal claddings (to test for different strengths).
Data is collected in terms of pressure (kPa), and number of wind cycles (Ni).
Factors that contribute to failures
Strength of metal
Length of screws - causes failures, either pull-out or pull-through:
Pull-out
Occurs to small screws that are pulled out due to deflection.
Screw length should be
longer
than crest height so that the embedded length of the screw is sufficient to withstand high deflection
Pull-through
Causes fracture/split, thus is more concerning than pull-out failure because it leads to cracks, then leads to leakage in a building
Hajar Azalia Binti Zainal
(2015990)