Some of the bridges that Lowcountry residents depend on during their journeys to and from work are getting a closer look.

The secret to their stability can be found under the bridges.

Cracks found in steel-plated girders supporting four Interstate 77 bridges have prompted the state to investigate the condition of 16 Lowcountry spans to see if there is a similar problem here.

So far, 10 of the area bridges this week passed an inspection ordered by Transportation Secretary Buck Limehouse. Four bridges in North Charleston will be inspected by Tuesday, as will one bridge in Jasper County and another in Beaufort County, the state Department of Transportation reported Thursday.

"We felt it was the proper thing to do," DOT spokesman Pete Poore said.

The North Charleston bridges yet to be inspected were identified as an Interstate 26 span over railroad tracks to South V.C. Chemical Co., a ramp onto I-26 east from Spruill Avenue, a ramp off I-26 west to Spruill Avenue and a ramp from I-26 east to Mount Pleasant Street, the DOT said.

The Beaufort County bridge of concern is on U.S. Highway 21 at Whale Branch, and in Jasper County an Interstate 95 bridge is marked for inspection, DOT said.

Limehouse said the agency would err on the side of caution to protect the public by evaluating bridges of similar age and design as the ones with cracked steel beams on I-77 in the Upstate. In all, state engineers identified 70 bridges for inspection. As of Thursday, 41 of the spans had received a clean bill of health.

On Tuesday, bridge inspectors found cracks in some girders supporting two bridges on I-77. The cracking was discovered on four beams on the northbound I-77 bridge and one beam on the southbound I-77 bridge over S.C. 901 in York County.

At another Upstate location, the DOT plans to replace steel girders supporting northbound and southbound bridges on I-77 in Chester County at Exit 62. Cracks were found in the girders when they were inspected April 29.

"Despite the appearance of the cracks, inspectors have determined that there is no immediate danger to the public and the bridges on I-77 will remain open," Limehouse said.

Limehouse has enacted emergency procurement procedures to speed replacement of the cracked girders. "We are moving forward quickly with this emergency project to protect the public. The condition of the girders is not life-threatening at this time, but the test results have prompted us to take the extra step of replacing all girders in both spans to ensure the safety of the public and to avoid the added expense of replacing remaining girders in the near future."

Local bridges inspected this week to see if there was cracking in girders were identified as I-26 over Southern Railway, I-26 to Baker Hospital S-222, an I-26 ramp to Mall Road, Interstate 526 northbound and southbound bridges over S.C. Highway 61, U.S. Highway 17 over S.C Highway 700, and I-26 over Milford Street & Koppers railroad. All of those bridges were found to be OK.

In Dorchester County, Interstate 95 northbound and southbound bridges over U.S. 178 were inspected for cracking but found to be in good shape.

Most of the bridges inspected were built in the 1960s and 1970s. The type of steel used for bridge girders changed in the 1980s, Poore said.