• Project sponsored by Dunning Thornton Consultants.• St Gerard’s Monastery was constructed in 1931 as an extension to an

existing 1908 church.• Three-storey structure located on Mount Victoria, Wellington.• Irregular arrangement of shear walls and columns.• Primarily consists of reinforced concrete column and beam frame with

infill panels of fired clay brick masonry.• St Gerard’s is a Category One heritage building and sits on NZS1170

Class B soil (Rock) and in a NZS3101 B2 (Coastal Frontage) environment.

Background

Structural Evaluation of St Gerard’s MonasteryM. R. Braun and J. P. PatersonSupervisors: R. P. Dhakal and A. G. Cattanach

Department of Civil and Natural Resources Engineering

The objectives of this project are to:Assess reinforcement details of major structural components of St Gerard’s Monastery and compare against current reinforced concrete member design requirements;Model and analyse typical structural components of the monastery to estimate their seismic performance and compare with expected performance of modern structures;Identify the deficiencies and assess vulnerability to propose potential retrofit options to minimise or reduce associated risk.

Objectives

Methodology

• Round bars are present throughout the structure.• Minimal ductility assumed as inelastic behaviour concentrated over small

region (potentially one crack) for round bars.• Yield stress of stirrups assumed as 480 MPa (Number 6 Wire), not tested.• Yield stress of longitudinal bars assumed 250 MPa, tested.• Some reinforcing and section details assumed with expert industry

guidance, as drawings incomplete.• Frame component considered fixed base as tied into floor diaphragm.

Limitations and Assumptions

Material Assessment: Material testing suggested St Gerard’s Monastery has good quality steel within its members. Some concrete elements will need to be repaired to ensure the building has a foreseeable residual life.Reinforcement Details: Comparing St Gerard’s reinforcement details to current design requirements highlighted a trend of insufficient density of transverse steel and near minimum amounts of longitudinal steel.Structural Components: Analysis of a typical frame component under modern earthquake requirements suggested that the frame component had a CDR of 0.43. This significant deficiency highlights the inadequate longitudinal and transverse reinforcement used in older buildings. It should be noted the frame component is under very light axial load, constituting primarily of a lightweight timber roof structure. The likelihood of joint failure is high given the poor detailing and lack of stirrups.

Conclusions and RecommendationsStructural members were identified on each floor and overlaid to see how loads are transferred through the building and into the foundations. This identified key structural elements.

Load Path Assessment

GroundFirstSecondFull Height Members

N

S

EW

• Comprehensive review of relevant chapters of NZS3101:2006 undertaken.• Standard details compared to code minimum and maximum limits.• Common trend of inadequate area and spacing of transverse steel.

NZS3101 Review and Comparison

Note: Table is only an excerpt, listing only typical column deficiencies.

Material Assessment

Short Bar (Vertical)

Long Bar (Horizontal)

• Site Inspection to view structural condition.• Concrete Durability Assessment undertaken

by Opus found:• Carbonation well established in concrete• Variable levels of chloride contamination• Average cover concrete as low as 15 mm• Foreseeable residual life with maintenance

• Steel Testing conducted at UC:• Two samples extracted, ½ inch round bar• Tension test until failure• fy = 280 MPa, fu = 430 Mpa, E = 201 GPa

Completed Partially Completed To Be Completed

Structural Seismic AnalysisNorthern Elevation Frame Component

Frame Analysis • NZS1170.5 ‘parts’ method used to find

seismic demand for the top floor frame component.

• SAP2000 elastic analysis used to find member demands.

• Moment-axial force interaction and shear capacity calculated for beams and columns.

• Capacity Demand Ratio’s (CDR’s):• Column flexural CDR = 0.43• Column shear CDR = 1.46• Beam flexural CDR = 1.50• Beam shear CDR = 2.04

Note: Shear capacity calculated in non-plastic hinge zone assuming full contribution from concrete. When concrete is damaged, it cannot be relied on for shear resistance, lowering the CDR.

Typical Frame

Typical wall

Review current reinforced concrete requirements set out in NZS3101:2006.

Assess typical frame component.

Assess typical structural wall.Review St Gerard’s

drawings and extract typical reinforcement details.

Assess adequacy or inadequacy of reinforcement details.

Suggest retrofit solutions based on deficiencies and vulnerabilities.

Assess current structural condition through material assessment.

2017 RDH02 I-6

Completion status as of 15 September 2017