**7.5 Silver Suspension Bridge**

The Silver Bridge, **Figure 11**, at Point Pleasant WVA, crossing over to Gallipolis, Ohio, over the Ohio River, opened in 1928, **Figure 10**, and was the first bridge un the US to use the eye bar-link suspensions system. At 5 p.m. 15 December 1967, a single eye bar failed causing the bridge to collapse in seconds, killing 46.

*Failure analysis*: A cleavage fracture in lower limb of the eye of eye bar 330 was the cause of the bridge failure. The single-point failure caused entire bridge to collapse. The contributing factors were the fact the bridge had no redundancy, the cracked eye in the eye bar was not found during routine inspections, and the combined action of

**Figure 11.** *The Silver Bridge in 1928, as failed in December 1967. CC BY-SA 3.0.*

stress corrosion and corrosion fatigue over 40 years. As result the US Congress passed a federal law requiring systematic inspection of all US bridges.

#### **7.6 I-880 Cypress Freeway Collapse**

The Loma Prieta earthquake in 1989 caused heavy damage in Santa Cruz County which collapsed the double-deck Cypress Street Viaduct, **Figure 12**, of Interstate 880 in West Oakland. The 6.9 magnitude earthquake caused 63 deaths and 375 injuries.

Moehle [10] states the viaduct was built-in the late 1950s on reclaimed marsh land the Cypress Street Viaduct was a double-deck freeway section made of non-ductile reinforced concrete. The Viaduct was designed as a two-tier multi-lane highway constructed of reinforced concrete upper and lower levels were connected by twocolumn bents in a combination of cast concrete and four pin (shear key) connections. The upper deck in some sections was not securely fastened to the lower deck, making this concrete susceptible to vibrations [10].

Yashinsky [11] indicates two major factors led to the collapse. The first was the geotechnical aspect of the central San Francisco Bay area. The second was the design of the concrete columns and bent caps and pin connections. Strong ground shaking in the marshland caused soil liquefaction. As the bridge vibrated during the earthquake, the pins connecting the upper level to the lower level also began to vibrate, causing the concrete surrounding the pins to crumble and break away. Without the presence of concrete under the support columns, the columns slid sideways under the weight of the upper deck and allowed a large portion of the upper deck to collapse [11].

*Failure analysis*: The root cause of the collapse of the Cypress Express Freeway was failure of pins connecting the upper and lower levels due to the strong ground shaking. Contributing factors were inadequate transverse reinforcement in the columns and deficient bent cap and pin connection designs and lack of compensation for the weak soil conditions [11].

Tests were performed by Monteiro et al. [12] on pieces of concrete extracted from the wreckage to assess structural integrity; many components of the Viaduct were found to be structurally sound. It was concluded that the concrete used had more than satisfactory strength. In addition, micro structural analysis of concrete

**Figure 12.** *Collapse of the I-880 freeway in the 1989 Loma Prieta earthquake. CC BY-SA 3.0.*

#### *Failure Analysis – Structural Health Monitoring of Structure and Infrastructure Components*

samples taken from undamaged columns within the region of collapse showed that the concrete was produced and cast according to the proper procedures at the time of construction [12].
