Brave volunteers and staff took a crack at the safety of a glass bottom bridge in China at the weekend before it opens to the public. They tested the structure suspended 300 meters (984 feet) above the Zhangjiajie Grand Canyon in Zhangjiajie National Park of central Hunan province, by hitting some of the glass panels with sledgehammers.On Saturday morning, around 20 volunteers and staff were taken to the 430-meter-long bridge and harnessed to its sides as a precaution. They hit some of the panels with sledgehammers and afterwards a 15-tonne (33069.3 pounds) SUV was driven over them, showing the structural strength of the glass panels.None of the volunteers were able to smash completely through the glass, which mostly broke into pieces. The volunteers were later invited to walk over the shards and damaged panels.An investor founded Zhangjiajie Grand Canyon Co. Ltd to to carry out the project and has put a total of around 250 million yuan ($39 million) into the bridge's construction. The creators claim it is the largest of its kind in the world.Construction on the bridge began in June of last year. Zhangjiajie National Park has not announced an official public opening date for the bridge, but Chinese media has reported it will be in July this year.Safety has been an issue at another glass bridge in China. Last October, tourists at Yuntai Mountain Park in northern Henan province reported cracks in a glass panel. Since then, the Yuntai Mountain Park bridge has been closed for maintenance.