I used this script to read a few months worth of my IIS logs to create a single log file. I used the single file for load testing with Web Application Stress tool.
$a = gci -Path C:inetpubiislogs3.comwwwlogstest -Filter *.log
foreach($file in $a)
Write-Host “Processing – $file”
$a = gc $file.FullName
Add-Content -Path c:temploadtest.log -Value $a