Date of this Version
Maguire, M., Al-Rubaye, S. (2022) "Tilt-Up Partially Composite Insulated Wall Panels" Report to the Tilt-Up Concrete Association, Mount Vernon, IA.
This research project was initiated to investigate the behavior of load-bearing concrete insulated wall panels for use in tilt-up construction. The primary objective was to understand the inelastic behavior of these panels so that engineers could perform a proper second-order analysis for combined axial and out-of-plane loading. Toward this aim, the Tilt-up Concrete Institute (TCA) and wythe connector suppliers Innstruct, Thermomass, HK Composites, Dayton Superior, and IconX, funded this study.
This report contains information related to testing of solid and partially composite insulated wall panels that integrated proprietary wythe connection systems. Using the information from these tests, a method to predict out-of-plane moments and deflection suitable for second-order slender wall analysis was proposed for insulated walls. Additionally, the shear flow approach, was found to be inaccurate and a new method for predicting horizontal shear failure was introduced. The new methods are demonstrated and compared to testing data and found to be accurate and conservative.
Since tilt-up panel testing of similar scope had not been done since the 1980s on panels of lower height, there were several goals for this testing. This represented an opportunity to validate the current ACI code alternate slender wall analysis method and provide a set of control panels for testing solid tilt-up panel behavior. Testing solid panels and CIPs of 40 ft span, a length typical of contemporary construction, was critical so that such slenderness ratios could be observed and significant second-order panel behavior could be identified.
As part of this, the research team created a modified version of the slender wall design method to predict second-order load and deflection behavior in the post-cracking range in CIPs. For solid panels, the 1980s testing program popularized the “slender wall design method” outlined in ACI 551 and the goal of this newer methodologies is to do the same for CIPs. Additionally, horizontal shear failure analysis methods were investigated to enable design against such failures.
Solid panel deflections and strength were as expected and matched very well the tilt-up Slender Wall Design method. Furthermore, cracking stresses were observed close to the (2/3)fr stipulated by the Slender Wall Method. For the CIPs, the two primary failure modes were observed: flexural reinforcement yielding and horizontal shear failure. The Group A panels performed very similarly to solid walls, even matching closely an unmodified version of the Slender Wall Design Method. This behavior was likely due to the reduced and solid regions noted in the Group A panels that would be similar to their in-service construction. The Group B, C, D, and E panels all experienced both flexural and shear failures in different specimens and required the use of a separate set of analysis methods that would also be applicable to Group A panels. The following describes the methods recommended for all panel types tested herein.
Using the unique experimental information herein, The Shear Flow method and a new method termed The Shear Slip Method were evaluated to estimate horizontal shear failure. The Shear Flow method, when used properly, results in perhaps an overlyconservative prediction of horizontal shear strength but did not match the observed data well. The Shear Slip Method relies on an assumption of the failure slip mechanism (as observed from these and other experiments) and the double shear data to determine a maximum horizontal shear strength while incorporating the ductility of the connectors. This method was found to predict horizontal shear failure both accurately and conservatively.
A Modified Slender Wall Method was developed that estimates the contribution of connector slip to the shear deformations in a straightforward way. When using this method to predict the deformations at failure for panels that experienced flexural failure it produced accurate and conservative results. For panels that are controlled by horizontal shear failure, this method can be overly conservative for flexural deformations because it is intentionally simplified. Another method termed the K123 method was demonstrated that can better predict panel deflections and horizontal shear failures using matrix analysis or other methods. This method is not recommended without further validation but does demonstrate panel load and deformation behavior well.