Diego Pizarro Pohl


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Pizarro Pohl

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Diego

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0009-0009-7342-4051

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2022 - 20259
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Publications 1 - 9 of 9
  • Cyclic Tests Performed on Real-Scale Squat Reinforced Concrete Shear Walls: Transition between Diagonal Shear and Sliding Shear Controlled Behavior Modes
    Item type: Journal Article
    Pizarro Pohl, Diego; Kovarbašić, Milan; Stojadinovic, Bozidar (2025)
    Journal of Structural Engineering
    Squat reinforced concrete shear walls are commonly used as primary gravity and lateral load–resisting systems in structures. Such low aspect ratio walls respond to load in diagonal or sliding shear. A series of real-scale quasi-static cyclic shear wall tests with identical geometry were conducted at the Multi-Axial Subassemblage Testing (MAST) facility at ETH Zürich to identify the influence of the axial load ratio and the steel reinforcement ratios on the transition between diagonal shear and sliding shear controlled behavior modes. Two specimens failed in sliding shear, and the other two failed in shear, either in diagonal compression or diagonal tension. The tests showed that squat walls exhibiting a sliding shear failure remain stable under the applied axial load even at displacements corresponding to 2% drift ratio. On the other hand, the walls that failed in diagonal shear did so in a brittle manner at displacements corresponding to 1% drift ratio. However, walls that slid had large residual displacements. The values of the shear wall axial load ratio and the longitudinal and horizontal reinforcement ratios at the transition between shear and sliding were identified.
  • Displacement prediction equations for seismic design of single friction pendulum base‐isolated structures
    Item type: Journal Article
    Silva, Andréia; Pizarro Pohl, Diego; Stojadinovic, Bozidar (2024)
    Earthquake Engineering & Structural Dynamics
    We propose a set of equations for preliminary risk-targeted seismic design of structures base-isolated using single friction pendulum (SFP) bearings. The equations offer statistical estimates of the maximum displacement of the superstructure relative to the base and the maximum displacement of the isolated base response quantities of interest (RQIs), given ground motion intensity measures and the essential dynamic properties of the SFP bearing base-isolated structure. The set of proposed equations enables preliminary seismic design of SFP base-isolated structures using the mean annual frequency of exceeding displacement-defined limit states related to the two RQIs. To develop the design equations, we define and use a two-degree-of-freedom (2DOF) surrogate model that features a few essential dynamic parameters of the SFP bearing base-isolated structure. We first verify that the 2DOF surrogate model is accurate enough to represent the base and superstructure displacements compared to the complete multiple-degree-of-freedom model of the prototype SFP bearing base-isolated structure. Next, we perform more than 5 million non-linear dynamical analyses of 4900 distinct 2DOF surrogates subjected to 210 different recorded ground motions scaled five times. We fit the response data of each 2DOF surrogate to a linear model and use two different modeling techniques to derive the design equations. One model is based on Polynomial Chaos Expansion (PCE), and the other model is based on Linear Regression (LR). The PCE model is more accurate than the LR model, with the trade-off regarding its simplicity. Nevertheless, both the PCE and the LR models are accurate enough to estimate the design quantities of interest of the SFP bearing base-isolated structure for preliminary design purposes. Lastly, we exemplify the use of the proposed design equations and we show that the estimate of base displacement is conservative in the cases when the superstructure of the SPF bearing base-isolated structure yields.
  • Multi-Axial Subassemblage Testing System for Hybrid Simulation With Large-Scale Structural Components
    Item type: Journal Article
    Pizarro Pohl, Diego; Kovarbašić, Milan; Abbiati, Giuseppe; et al. (2025)
    Earthquake Engineering & Structural Dynamics
    This article presents the Multi-Axial Subassemblage Testing facility of ETH Zurich, Switzerland (ETHZ-MAST) for quasi-static testing and hybrid simulation (HS) of large-scale structural components and assemblies. The ETHZ-MAST features a 6-degrees-of-freedom (DOFs, 3 translations and 3 rotations) loading system based on a steel crosshead and 10 hydraulic actuators. The control system of the test system allows for mixed-mode control of applied boundary conditions meaning that some DOFs can be controlled in force while the remaining are controlled in displacement. The control system relies on a kinematic model of the system and compensates for the elastic deformation of the crosshead and the backlash in the actuator clevises. The capabilities of the facility are demonstrated with two experimental campaigns on reinforced concrete shear walls, which comprise in-plane quasi-static cyclic testing and HS of nominally identical axially loaded specimens. One of the campaigns studied the transition between flexure and rocking behavior modes in specimens with spliced reinforcement, whereas the other addressed the transition between shear and sliding behavior modes. A comparison between the testing protocols revealed that the specimens tested in HS using a ground motion excitation had a larger displacement capacity than the nominally identical specimens tested using a quasi-static cycling test protocol. However, the behavior mode transitions the specimens exhibited did not depend on the test protocol, but on the specimen strengths and the applied axial loads.
  • Cyclic and hybrid tests on real-scale RC shear walls: Transition between shear and sliding failures
    Item type: Conference Paper
    Pizarro Pohl, Diego; Kovarbasic, Milan; Stojadinovic, Bozidar (2024)
    Reinforced concrete shear walls have seismic failure modes such as bending, shear, sliding, or rocking. Which failure mode occurs depends on the wall parameters such as its boundary conditions, geometry, axial load, reinforcement ratios, and material characteristics, as well as on the lateral loading time history. In particular, squat walls are prone to fail in shear or sliding. There is some uncertainty, due to the lack of experimental data, on how squat wall parameters define their failure modes. A series of real-scale shear wall tests were conducted at ETH Zurich to identify the transition between shear and sliding failures. The response analysis of two sets of specimens with same geometry and reinforcement ratio, but different levels of axial load and different load history, is presented. One set of specimens was tested using a quasi-dynamic incrementally increasing displacement protocol, while the seismic response of the other set to an earthquake ground motion was simulated using hybrid model. The hybrid simulation specimen with an axial load ratio of 4.02%, HSW01, failed in sliding, with a peak strength of 2729 kN, while the hybrid simulation specimen with axial load ratio of 8%, HSW02, failed in compression diagonal shear with a peak strength of 3359 kN. The single degree of freedom system with specimen HSW01 had 78 mm of top displacement, whereas specimen HSW02 had 15 mm in response to the same ground motion. A comparison with the results of the nominally identical specimens tested quasi-cyclically allowed to relate previously identified damage states to levels of ground motion intensity. The four tests show that squat walls exhibiting a sliding failure remain stable, in that they continue to carry their axial load, as opposed to the walls that failed in shear. However, walls that slid moved significantly more.
  • Low Aspect Ratio RC Shear Walls with Lap Splices: Seismic Performance and Design Implications
    Item type: Conference Paper
    Kovarbasic, Milan; Pizarro Pohl, Diego; Stojadinovic, Bozidar (2024)
    World Conference on Earthquake Engineering Online Proceedings ~ Proceedings of the 18th World Conference on Earthquake Engineering (WCEE 2024)
    Reinforced concrete (RC) shear walls are frequently used as lateral load-resisting elements in RC structures in seismic regions. Hence, reliable evaluation of the displacement capacity of these elements is essential for the performance-based seismic design. An experimental campaign on low aspect ratio RC shear walls with lap splices was conducted at ETH Zürich to investigate their seismic-performance and collect data for the development and validation of numerical models for the displacement-based seismic assessment. The campaign includes quasi-static cyclic (QSC) and hybrid simulation (HS) tests. It was found that the tension failure of the lap splices caused a progressive cyclic strength degradation of the walls and the transition from flexural to rocking mode of behaviour. Once the rocking occurred, the walls were able to sustain significant ductility demands showing at the same time no signs of additional damage or loss of the axial load bearing capacity. Further, the approaches for numerical modelling and assessment of RC shear walls with lap splices are presented and discussed.
  • Experimental investigation of the sliding failure mode in full-scale squat reinforced concrete shear wall specimen
    Item type: Conference Paper
    Pizarro Pohl, Diego; Kovarbasic, Milan; Stojadinovic, Bozidar (2022)
    Proceedings of the Third European Conference on Earthquake Engineering and Seismology – 3ECEES
    Squat-reinforced concrete shear walls are used as a gravity and lateral load resisting system in structures such as buildings and nuclear power plants. Due to their low aspect ratio, they are prone to shear or sliding failure. A shear wall was subjected to a cyclic test at the new Multi-Axis Sub-Assemblage Testing (MAST) facility at ETH Zurich. The shear to span ratio was 0.51 and a vertical load of 5.61% of the axial capacity of the wall was applied. The wall had a sliding failure, with a peak load capacity of 2760 kN. Digital Image Correlations (DIC) results show how the shear crack developed until sliding started and, from this point on, the majority of the wall deformation originated in the wall-foundation interface. Sliding displacements consisted of more than 50% of the total displacements of the specimen in large-amplitude cycles.
  • Hybrid Simulation Tests of Real-Scale Squat Reinforced Concrete Shear Wall Specimens
    Item type: Journal Article
    Pizarro Pohl, Diego; Kovarbašić, Milan; Stojadinovic, Bozidar (2025)
    Journal of Structural Engineering
    Squat reinforced concrete shear walls usually have diagonal shear- or sliding shear-controlled behavior. Due to the lack of experimental data, there is uncertainty on how squat wall design parameters define their behavior modes. Two real-scale tests were conducted at ETH Zurich on specimens of equal geometry and reinforcement, but different axial load ratios (ALR), employing hybrid simulation techniques to apply recorded ground-motion excitation in a quasi-dynamic manner. Specimen HSW01 had an ALR of 4.02%, whereas the ALR for Specimen HSW02 was 8%. Specimen HSW01 failed in sliding shear, exhibited a quasi-ductile behavior, developed a peak resistance of 2,730 kN, and reached a displacement corresponding to a 3% drift ratio without losing the ability to carry its axial load. Specimen HSW02 failed in shear diagonal compression and lost the ability to carry its axial load at a horizontal displacement corresponding to a 2% drift ratio and a peak resistance of 3,360 kN. The crack patterns, crack width, and damage progression observed in both tests are presented. Finally, the results were compared with similar specimens tested using a displacement-driven incremental symmetric quasi-static cyclic test protocol. Hybrid simulations using recorded ground-motion excitation did not affect the failure mode of the specimens but allowed them to sustain larger displacements than those tested cyclically.
  • Crack Kinematics During the Transition from Shear to Sliding or Crushing Failure in Seismically Loaded Squat Reinforced Concrete Shear Walls
    Item type: Conference Paper
    Pizarro Pohl, Diego; Kovarbasic, Milan; Stojadinovic, Bozidar (2023)
    Lecture Notes in Civil Engineering ~ Building for the Future: Durable, Sustainable, Resilient
    Squat reinforced concrete shear walls are used as gravity and lateral-load-resisting systems in structures such as residential buildings or nuclear power plants. Due to their low aspect ratio, they are prone to failing in shear or sliding. There is uncertainty on which parameters define this failure mode transition, and how to account for this in the design of new buildings or assessment of existing structures. A series of real-scale shear wall tests are being conducted at the multi-axis subassemblage testing (MAST) facility at ETH Zürich to identify the transition between shear and sliding failures. Response analysis of two specimens with the same geometry and reinforcement ratio, but different levels of axial load is presented. Specimen SW01 failed in sliding, whereas Specimen SW02 failed in shear (diagonal compression). Their peak horizontal shear strengths were 2460 kN and 2980 kN, respectively. The evolving kinematics of the cracks developed in both specimens is analyzed using the deformation fields obtained with digital image correlation (DIC) measurements and compared to identify the point of shear-to-sliding and shear-to-compression transitions.
Publications 1 - 9 of 9