WHB Engineers was tasked with both strengthening an existing tank as well as designing a new 7.5 MG circular, prestressed concrete tank and pump station improvements.  The City was concerned that their current tank could potentially fail after a similar design in another jurisdiction made headlines in 1998 with a catastrophic failure. 

WHB Engineers managed the design for temporarily strengthening the original tank by installing steel strands along the exterior upper and lower areas of the tank. 

WHB Engineers then prepared the plans, specifications, and estimates for a new tank designed in accordance with California Building Code, ASCE 7, AWWA D110.  WHB Engineers was responsible for completing both the structural design along with EI&C, mechanical, and water quality.

WHB Engineers operating company, conducted a seismic assessment for the City of Redlands. The City of Redlands selected Brady to complete a seismic assessment of eighteen (18) of the City’s potable water storage reservoirs, seven (7) pump stations, and two (2) transmission mains for the Water Division.

The work involved a study of existing interior and exterior conditions, a seismic code assessment, recommended improvements, a hydraulic analysis of the entire system with an eye on reservoir consolidation opportunities, and a budget level cost.

WHB Engineers performed structural analyses on concrete, steel, and prestressed reservoirs. The City of Redland lies between the San Andreas and San Jacinto faults. All analyses were conducted with site-specific seismic reports and considered the current and anticipated forthcoming (ASCE 7-22) requirements of the seismic code. 

WHB Engineers provided recommendations of reservoir replacements and upgrades. To save considerable time and expense for the City, each reservoir was studied using WHB Engineers underwater drone. Interior roof inspections were completed via an inflatable boat. WHB Engineers provided confined space entry support with WHB Engineers staff. 

The project included the assessment of pipe transmission mains critical to the treatment plant influent. These critical pipelines were observed to have structural and seismic vulnerabilities. Recommendations were made to assure that safe, reliable water can be supplied to the City’s water treatment plants.

This study included the assessments, inspection, analysis, design upgrades,
and cost-estimates for 45 water storage facilities including 22 steel tanks and 23 concrete tanks. The inspection included interior ROV inspection, WHB Engineers operating company, self-performed. The analysis was performed using site-specific seismic values to satisfy the current Code as well as addressing upcoming seismic requirements. Analysis was performed considering the latest editions of AWWA, ACI, CBC, and ASCE 7 documents.

As is commonly the case in California, many steel tanks were constructed without anchorage and with insufficient freeboard. Careful analysis supported a measured reduction in water level to comply with current Code. Having a specialty in prestressed tanks, WHB Engineers leveraged an expertise to carefully review the circumferential and vertical prestressing in order to confirm the level of compression in the concrete corewall. This was used to determine the watertightness of the tank.

After careful assessment, each tank was assigned a grade, a priority, and a cost to upgrade. Upgrade options were estimated and prioritized. Connections to the tanks were also reviewed for resilience during earthquakes. Seismic-induced earth settlement would likely cause a differential displacement between the tank and its pipe connections. Historically, this has been a failure mechanism during strong ground motion. Special pipe fittings which can accommodate differential settlement were recommended and need to be carefully specified in order to function correctly.

Two final tables were produced for the deliverable; one for Los Angeles County and one for Ventura County. These tables with the supporting cost-estimates and calculations will be used to support Rate Case decisions for hundreds of thousands of customers. Customers of the California American Water can now have confidence in a road map for the reliable distribution of water.