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F.J. Noortman
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1
Applicability of the Pushover Method for the Seismic Assessment of URM Structures in Groningen
A Case Study of a Low-Rise Apartment Building
In Groningen, seismic activity has increased due to the extraction of gas in the area. A large-scale research campaign has been launched with the aim to assess and safeguard structures in the region. However, an accurate assessment of these buildings turned out to be a challenge, due to the nonlinear behaviour of the masonry and the dynamic nature of a seismic load. A Nonlinear Time History (NLTH) analysis takes into account both these factors, but the computational demand of such a method is considerable. Another method that is widely used to analyse the seismic response of a structure is the Modal Response Spectrum (MRS) method. The computational demand of this method is considerably less compared to NLTH, but nonlinear material behaviour is only taken into account in an indirect manner via a behaviour factor, and the results are considered to be too conservative. A third method is the Nonlinear Pushover (NLPO) method. It takes nonlinear material behaviour into account and compared to NLTH, NLPO is computationally more efficient. Furthermore, an advantage is that it separates capacity from demand. Even though the NLPO method is commonly applied worldwide, its validity still needs to be proven for the Groningen case. Both objectives were studied by looking into a single case study, consisting of a low-rise URM apartment building. The behaviour of the structure is characterised by a weak and strong direction, in which the weak direction is characterised by a relatively low stiffness and lateral capacity compared to the strong direction. The seismic response of the structure is determined according to the MRS, NLPO and NLTH methods. Furthermore, the NLPO analyses are executed using two different computational discretisation methods, namely continuum FEM and macro EFM. DIANA is used as a FEM solver for the MRS, NLPO and NLTH analyses and 3MURI is used for the EFM model. Moreover, a modal and uniform lateral load pattern are taken into account for the NLPO analyses. The conclusions which are drawn from the case study can generally be applied to low-rise URM apartment buildings in Groningen. However, it must be noted that significant alterations in geometry and building materials might influence the results. Furthermore, modelling assumptions have been applied, and it is important to note that the possible influence of these assumptions, may partially limit the extent of the conclusions. Moreover, several limitations are inherent to the studied methods, and cannot be accounted for somehow. All analyses are performed by incrementally increasing the seismic load until one of the near collapse limit state criteria according to NPR 9998 is met. Furthermore, three target displacement methods are evaluated: the capacity spectrum method according to NPR 9998, the regular N2-method, included in the Eurocode 8, and an adaptation of the N2-method which is developed specifically for URM structures by Guerinni. The performance of the structure according to each of the methods is studied subsequently, by looking into the force-displacement behaviour, displacement profile and damage at failure, failure mechanisms and the maximum admissible seismic load. Two significant disadvantages of macro EFM were identified when comparing the results of the NLPO analyses using 3MURI and DIANA. First, the fact that out-of-plane behaviour is not taken into account in 3MURI could significantly influence the behaviour of a structure in terms of base shear capacity, which is especially true when structures are characterised by an extremely low total length of piers in the in-plane direction. Furthermore,DIANA allows for a more gradual softening behaviour, which helps the post-peak force redistribution. As a consequence, the maximum admissible seismic load according to DIANA could be higher. However, despite the two aforementioned disadvantages of the macro EFM method as implemented in 3MURI, all other relevant results of both methods are similar. The fact that the two identified disadvantages of 3MURI can only result in more conservative results, suggests that macro EFM, as implemented in 3MURI, is a suitable computational discretisation method for the seismic assessment according to the NLPO method for low-rise URM apartment buildings in Groningen. However, it should be taken into account that the conservativeness of 3MURI could lead to a significantly larger amount of required retrofitting, in comparison with DIANA. The applicability of the NLPO method is reviewed by comparing the results of the MRS, NLPO and NLTH methods. Similar behaviour of the structure according to the NLPO and NLTH method was captured, which suggests that the NLPO method is a suitable analysis method for the studied typology. The maximum admissible seismic load using the target displacement method according to NPR 9998 is in-line with the NLTH analysis. However, the governing load case made use of a uniform load pattern, which returns a structural behaviour different than that obtained by NLTH analyses, as can be seen from the force-displacement behaviour. If only the capacity curve according to the modal load pattern would be considered, then the allowable seismic load according to NLTH is similar to that of NLPO using the target displacement method of Eurocode 8. Furthermore, from the results of the case study can be concluded that the choice of target displacement method has a significant influence on the maximum admissible seismic load. For the case study, NPR 9998 is more conservative in the strong direction, and Eurocode 8 is more conservative in the weak direction. Regarding the MRS method, very conservative results were found. A reason that was found for these conservative results is that the prescribed behaviour factor by NPR 9998 is too low for the case study when compared to that derived from the NLPO analysis. However, even with a larger behaviour factor, the results according to the MRS method would still be conservative in the weak direction.
...
In Groningen, seismic activity has increased due to the extraction of gas in the area. A large-scale research campaign has been launched with the aim to assess and safeguard structures in the region. However, an accurate assessment of these buildings turned out to be a challenge, due to the nonlinear behaviour of the masonry and the dynamic nature of a seismic load. A Nonlinear Time History (NLTH) analysis takes into account both these factors, but the computational demand of such a method is considerable. Another method that is widely used to analyse the seismic response of a structure is the Modal Response Spectrum (MRS) method. The computational demand of this method is considerably less compared to NLTH, but nonlinear material behaviour is only taken into account in an indirect manner via a behaviour factor, and the results are considered to be too conservative. A third method is the Nonlinear Pushover (NLPO) method. It takes nonlinear material behaviour into account and compared to NLTH, NLPO is computationally more efficient. Furthermore, an advantage is that it separates capacity from demand. Even though the NLPO method is commonly applied worldwide, its validity still needs to be proven for the Groningen case. Both objectives were studied by looking into a single case study, consisting of a low-rise URM apartment building. The behaviour of the structure is characterised by a weak and strong direction, in which the weak direction is characterised by a relatively low stiffness and lateral capacity compared to the strong direction. The seismic response of the structure is determined according to the MRS, NLPO and NLTH methods. Furthermore, the NLPO analyses are executed using two different computational discretisation methods, namely continuum FEM and macro EFM. DIANA is used as a FEM solver for the MRS, NLPO and NLTH analyses and 3MURI is used for the EFM model. Moreover, a modal and uniform lateral load pattern are taken into account for the NLPO analyses. The conclusions which are drawn from the case study can generally be applied to low-rise URM apartment buildings in Groningen. However, it must be noted that significant alterations in geometry and building materials might influence the results. Furthermore, modelling assumptions have been applied, and it is important to note that the possible influence of these assumptions, may partially limit the extent of the conclusions. Moreover, several limitations are inherent to the studied methods, and cannot be accounted for somehow. All analyses are performed by incrementally increasing the seismic load until one of the near collapse limit state criteria according to NPR 9998 is met. Furthermore, three target displacement methods are evaluated: the capacity spectrum method according to NPR 9998, the regular N2-method, included in the Eurocode 8, and an adaptation of the N2-method which is developed specifically for URM structures by Guerinni. The performance of the structure according to each of the methods is studied subsequently, by looking into the force-displacement behaviour, displacement profile and damage at failure, failure mechanisms and the maximum admissible seismic load. Two significant disadvantages of macro EFM were identified when comparing the results of the NLPO analyses using 3MURI and DIANA. First, the fact that out-of-plane behaviour is not taken into account in 3MURI could significantly influence the behaviour of a structure in terms of base shear capacity, which is especially true when structures are characterised by an extremely low total length of piers in the in-plane direction. Furthermore,DIANA allows for a more gradual softening behaviour, which helps the post-peak force redistribution. As a consequence, the maximum admissible seismic load according to DIANA could be higher. However, despite the two aforementioned disadvantages of the macro EFM method as implemented in 3MURI, all other relevant results of both methods are similar. The fact that the two identified disadvantages of 3MURI can only result in more conservative results, suggests that macro EFM, as implemented in 3MURI, is a suitable computational discretisation method for the seismic assessment according to the NLPO method for low-rise URM apartment buildings in Groningen. However, it should be taken into account that the conservativeness of 3MURI could lead to a significantly larger amount of required retrofitting, in comparison with DIANA. The applicability of the NLPO method is reviewed by comparing the results of the MRS, NLPO and NLTH methods. Similar behaviour of the structure according to the NLPO and NLTH method was captured, which suggests that the NLPO method is a suitable analysis method for the studied typology. The maximum admissible seismic load using the target displacement method according to NPR 9998 is in-line with the NLTH analysis. However, the governing load case made use of a uniform load pattern, which returns a structural behaviour different than that obtained by NLTH analyses, as can be seen from the force-displacement behaviour. If only the capacity curve according to the modal load pattern would be considered, then the allowable seismic load according to NLTH is similar to that of NLPO using the target displacement method of Eurocode 8. Furthermore, from the results of the case study can be concluded that the choice of target displacement method has a significant influence on the maximum admissible seismic load. For the case study, NPR 9998 is more conservative in the strong direction, and Eurocode 8 is more conservative in the weak direction. Regarding the MRS method, very conservative results were found. A reason that was found for these conservative results is that the prescribed behaviour factor by NPR 9998 is too low for the case study when compared to that derived from the NLPO analysis. However, even with a larger behaviour factor, the results according to the MRS method would still be conservative in the weak direction.
Quidico Bay
Design Proposal for a Fishing Harbour in the bay of Quidico
Student report
(2018)
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Falko Noortman, Mark Ruessink, Mathijs Mann, Ronald Verlinde, Wouter Sonnema, Lambert Houben, Dominique Ngan-Tillard, Henk Jan Verhagen, Mauricio Pradena Miquel
Quidico is a small town, approximately 200 kilometer south of Concepcion. In the bay adjacent to Quidico town, a great number of local fishermen are active. In the current situation, high waves, a strong current and significant sediment transport hamper the effectiveness of the bay as fishing harbour. Also qualitative onshore facilities to support onshore activities of the fishermen, are absent. The Department of Ports of theMinistry of Public Works, developed a preliminary design proposal, to solve these problems. However, after consultation with the fishermen, this proposal was declared unsatisfactory. Therefore, an additional study is performed to develop a new integral design for the bay of Quidico. The desired design consists of onshore buildings, a paved support area, mooring facilities and breakwaters to create shelter for safe mooring of the fishing boats. Furthermore, these breakwaters shouldmitigate the problems related to sediment transport.
To develop a new breakwater orientation and design, wave data is analysed. Waves coming from the south to south-west are most common, but not guiding due to the sheltering factor of IslandMocha, positioned in front of the coast. The guiding wave, which is coming from the north-west, is implemented in models of Delft3D to see what the new orientation of the breakwater should be. Based on the wave analysis, sediment transport analysis and modelling results, a new breakwater orientation is determined, that fulfills all requirements prescribed by the DoP. After defining this new orientation, the influence of the breakwater on sediment and waves is analysed. Due to the new orientation, a new design of the breakwater is made.
The fishing harbour should offer the possibility for the fisherman to unload their goods and berth safely. The DoP proposed the construction of a mooring facility along the south-west shoreline of Quidico Bay. Two types of quay walls for the mooring facilities are proposed, a sheet pile wall and a concrete mass wall. For both types a preliminary design is developed, by making use of the 2D finite element software PLAXIS and hand calculations. The preferred mooring facility design mainly depends on the soil conditions at the specific location. From the boundary conditions it is concluded the bedrock is found at a depth of 60m, the soil above mainly consists of sand. Therefore the construction a sheet pile wall to serve as mooring facility, is recommended.
In the initial design of the Department of Ports, six separate masonry buildings are proposed to accommodate the desired supporting facilities. These buildings cover a large area of the bay and will require a large paved supporting platform. To reduce this paved area, the DoP is interested in a more compact design, that includes all supporting facilities in one multi-storey building. In consultation with the DoP two different designs are developed; a three-storey steel building and a two-storey concrete building. A structural design is developed within the boundaries set by the functional design requirements. Next, a structural analysis is performed by making use of finite element software (ETABS) and a final design is obtained for both buildings. The concrete building is concluded to be the most suitable option for the DoP.
Quick offloading of the boats and smooth transshipment of goods is hindered due to the lack of a good support area and access road. The DoP proposed a design for both pavements in the their preliminary study, but it was requested to evaluate different alternatives. Three different pavement technologies are proposed for the access road: surface treatment, asphalt and concrete slabs. For the pavement in the support area concrete slabs are the preferred solution. To achieve an optimal pavement design that fulfills all structural and serviceability requirements throughout the full design life, slab pavements with different dimensions and thicknesses are evaluated. In conclusion, short concrete slabs are the preferred pavement for both areas. Short slab pavement is an upcoming technology that has great advantages in terms of structural performance and costs.
...
To develop a new breakwater orientation and design, wave data is analysed. Waves coming from the south to south-west are most common, but not guiding due to the sheltering factor of IslandMocha, positioned in front of the coast. The guiding wave, which is coming from the north-west, is implemented in models of Delft3D to see what the new orientation of the breakwater should be. Based on the wave analysis, sediment transport analysis and modelling results, a new breakwater orientation is determined, that fulfills all requirements prescribed by the DoP. After defining this new orientation, the influence of the breakwater on sediment and waves is analysed. Due to the new orientation, a new design of the breakwater is made.
The fishing harbour should offer the possibility for the fisherman to unload their goods and berth safely. The DoP proposed the construction of a mooring facility along the south-west shoreline of Quidico Bay. Two types of quay walls for the mooring facilities are proposed, a sheet pile wall and a concrete mass wall. For both types a preliminary design is developed, by making use of the 2D finite element software PLAXIS and hand calculations. The preferred mooring facility design mainly depends on the soil conditions at the specific location. From the boundary conditions it is concluded the bedrock is found at a depth of 60m, the soil above mainly consists of sand. Therefore the construction a sheet pile wall to serve as mooring facility, is recommended.
In the initial design of the Department of Ports, six separate masonry buildings are proposed to accommodate the desired supporting facilities. These buildings cover a large area of the bay and will require a large paved supporting platform. To reduce this paved area, the DoP is interested in a more compact design, that includes all supporting facilities in one multi-storey building. In consultation with the DoP two different designs are developed; a three-storey steel building and a two-storey concrete building. A structural design is developed within the boundaries set by the functional design requirements. Next, a structural analysis is performed by making use of finite element software (ETABS) and a final design is obtained for both buildings. The concrete building is concluded to be the most suitable option for the DoP.
Quick offloading of the boats and smooth transshipment of goods is hindered due to the lack of a good support area and access road. The DoP proposed a design for both pavements in the their preliminary study, but it was requested to evaluate different alternatives. Three different pavement technologies are proposed for the access road: surface treatment, asphalt and concrete slabs. For the pavement in the support area concrete slabs are the preferred solution. To achieve an optimal pavement design that fulfills all structural and serviceability requirements throughout the full design life, slab pavements with different dimensions and thicknesses are evaluated. In conclusion, short concrete slabs are the preferred pavement for both areas. Short slab pavement is an upcoming technology that has great advantages in terms of structural performance and costs.
...
Quidico is a small town, approximately 200 kilometer south of Concepcion. In the bay adjacent to Quidico town, a great number of local fishermen are active. In the current situation, high waves, a strong current and significant sediment transport hamper the effectiveness of the bay as fishing harbour. Also qualitative onshore facilities to support onshore activities of the fishermen, are absent. The Department of Ports of theMinistry of Public Works, developed a preliminary design proposal, to solve these problems. However, after consultation with the fishermen, this proposal was declared unsatisfactory. Therefore, an additional study is performed to develop a new integral design for the bay of Quidico. The desired design consists of onshore buildings, a paved support area, mooring facilities and breakwaters to create shelter for safe mooring of the fishing boats. Furthermore, these breakwaters shouldmitigate the problems related to sediment transport.
To develop a new breakwater orientation and design, wave data is analysed. Waves coming from the south to south-west are most common, but not guiding due to the sheltering factor of IslandMocha, positioned in front of the coast. The guiding wave, which is coming from the north-west, is implemented in models of Delft3D to see what the new orientation of the breakwater should be. Based on the wave analysis, sediment transport analysis and modelling results, a new breakwater orientation is determined, that fulfills all requirements prescribed by the DoP. After defining this new orientation, the influence of the breakwater on sediment and waves is analysed. Due to the new orientation, a new design of the breakwater is made.
The fishing harbour should offer the possibility for the fisherman to unload their goods and berth safely. The DoP proposed the construction of a mooring facility along the south-west shoreline of Quidico Bay. Two types of quay walls for the mooring facilities are proposed, a sheet pile wall and a concrete mass wall. For both types a preliminary design is developed, by making use of the 2D finite element software PLAXIS and hand calculations. The preferred mooring facility design mainly depends on the soil conditions at the specific location. From the boundary conditions it is concluded the bedrock is found at a depth of 60m, the soil above mainly consists of sand. Therefore the construction a sheet pile wall to serve as mooring facility, is recommended.
In the initial design of the Department of Ports, six separate masonry buildings are proposed to accommodate the desired supporting facilities. These buildings cover a large area of the bay and will require a large paved supporting platform. To reduce this paved area, the DoP is interested in a more compact design, that includes all supporting facilities in one multi-storey building. In consultation with the DoP two different designs are developed; a three-storey steel building and a two-storey concrete building. A structural design is developed within the boundaries set by the functional design requirements. Next, a structural analysis is performed by making use of finite element software (ETABS) and a final design is obtained for both buildings. The concrete building is concluded to be the most suitable option for the DoP.
Quick offloading of the boats and smooth transshipment of goods is hindered due to the lack of a good support area and access road. The DoP proposed a design for both pavements in the their preliminary study, but it was requested to evaluate different alternatives. Three different pavement technologies are proposed for the access road: surface treatment, asphalt and concrete slabs. For the pavement in the support area concrete slabs are the preferred solution. To achieve an optimal pavement design that fulfills all structural and serviceability requirements throughout the full design life, slab pavements with different dimensions and thicknesses are evaluated. In conclusion, short concrete slabs are the preferred pavement for both areas. Short slab pavement is an upcoming technology that has great advantages in terms of structural performance and costs.
To develop a new breakwater orientation and design, wave data is analysed. Waves coming from the south to south-west are most common, but not guiding due to the sheltering factor of IslandMocha, positioned in front of the coast. The guiding wave, which is coming from the north-west, is implemented in models of Delft3D to see what the new orientation of the breakwater should be. Based on the wave analysis, sediment transport analysis and modelling results, a new breakwater orientation is determined, that fulfills all requirements prescribed by the DoP. After defining this new orientation, the influence of the breakwater on sediment and waves is analysed. Due to the new orientation, a new design of the breakwater is made.
The fishing harbour should offer the possibility for the fisherman to unload their goods and berth safely. The DoP proposed the construction of a mooring facility along the south-west shoreline of Quidico Bay. Two types of quay walls for the mooring facilities are proposed, a sheet pile wall and a concrete mass wall. For both types a preliminary design is developed, by making use of the 2D finite element software PLAXIS and hand calculations. The preferred mooring facility design mainly depends on the soil conditions at the specific location. From the boundary conditions it is concluded the bedrock is found at a depth of 60m, the soil above mainly consists of sand. Therefore the construction a sheet pile wall to serve as mooring facility, is recommended.
In the initial design of the Department of Ports, six separate masonry buildings are proposed to accommodate the desired supporting facilities. These buildings cover a large area of the bay and will require a large paved supporting platform. To reduce this paved area, the DoP is interested in a more compact design, that includes all supporting facilities in one multi-storey building. In consultation with the DoP two different designs are developed; a three-storey steel building and a two-storey concrete building. A structural design is developed within the boundaries set by the functional design requirements. Next, a structural analysis is performed by making use of finite element software (ETABS) and a final design is obtained for both buildings. The concrete building is concluded to be the most suitable option for the DoP.
Quick offloading of the boats and smooth transshipment of goods is hindered due to the lack of a good support area and access road. The DoP proposed a design for both pavements in the their preliminary study, but it was requested to evaluate different alternatives. Three different pavement technologies are proposed for the access road: surface treatment, asphalt and concrete slabs. For the pavement in the support area concrete slabs are the preferred solution. To achieve an optimal pavement design that fulfills all structural and serviceability requirements throughout the full design life, slab pavements with different dimensions and thicknesses are evaluated. In conclusion, short concrete slabs are the preferred pavement for both areas. Short slab pavement is an upcoming technology that has great advantages in terms of structural performance and costs.