發送短信 : Openings in thin-walled steel structures

   _____     ___      _____    _    _     _____   
  / ___//   / _ \\   / ____|| | || | ||  / ____|| 
  \___ \\  | / \ || / //---`' | || | || / //---`' 
  /    //  | \_/ || \ \\___   | \\_/ || \ \\___   
 /____//    \___//   \_____||  \____//   \_____|| 
`-----`     `---`     `----`    `---`     `----`