Second Order Effects in Concrete Insulated Wall Panels

Insulated concrete panels (CIPs) have been used for over 60 years for their both structural and thermal resistance. The flexural behavior of CIPs has been investigated in recent years. The CIPs are rapidly becoming ubiquitous in the precast industry, and the tilt-up industry is initiating a study to determine their effectiveness as a tilt-up product. There are several known challenges associated with a tilt-up version of a partially composite wall and likely other unknown challenges. This study 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. This dissertation contains information related to the testing of solid and partially composite insulated wall panels that integrated proprietary wythe connection systems. 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 to observe such slenderness ratios and identify significant second-order panel behavior. In addition, 24 small-scale panels of 11 ft-long were monitored for shrinkage and tested under flexural load to determine the effect of shrinkage and the reinforcement ratio on the cracking moment and tension stiffening model. 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 overly conservative prediction of horizontal shear strength but does 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 to estimate 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. The results from the experimental program and the panels from the literature were used to calibrate the OpenSees model. A large parametric study consisted of 648 models using OpenSees to evaluate different lengths of CIPs and connector types that were outside of the experimental program scope to demonstrate the effect of the slenderness and axial load. The parametric study confirms that the proposed methods agree well with Opensees models and confirm the findings from the experimental program. This project’s findings serve as a foundation for developing a design guide for Tilt-up CIP

Experimental and Simplified Analytical Investigation of Full Scale Sandwich Panel Walls

Concrete sandwich wall panels have been used for decades in the precast concrete construction industry because of their thermal efficiency. To achieve full or partial-composite action in concrete sandwich panel walls, the engineer must obtain a percent composite action from a connector manufacturer, making some engineers uncomfortable. Engineers are dependent upon the recommendations given by the connector manufacturers to establish their designs. This project tested six full scale sandwich panel walls to evaluate the percent composite action of various connectors and compare the results to those provided by the composite connector manufacturers. This project aimed to validate current procedures using these methods, and to develop simpler, more efficient methods for predicting overall strength of this innovative building system. This study concluded that the reported degrees of composite action from each manufacturer are considered conservative in all instances for the connectors tested. Additionally, the intensity and type of connectors are important factors in determining the degree of partial composite action in a panel

Tilt-Up Partially Composite Insulated Wall Panels

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. 399 page

Percent Composite Action at Ultimate in Sandwich Wall Panel Connectors

Many engineers feel uncomfortable that they must currently rely on percent-of-composite-action values obtained from a connector manufacturer to achieve full or partial-composite action in prestressed concrete sandwich wall panels. Engineers are dependent upon these recommendations to establish their designs. This project tested six full-scale concrete sandwich wall panels to evaluate the percent composite action of various connectors. These resulting values were then compared to those provided by the composite connector manufacturers. This study concluded that the reported degrees of composite action from each manufacturer are considered conservative in all instances for the connectors tested in this study. Additionally, the intensity and type of connectors are important factors to be considered in determining the degree of partial composite action in a panel

Investigating Composite Action at Ultimate for Commercial Sandwich Panel Composite Connectors

To achieve full or partial-composite action in prestressed concrete sandwich panel walls, the engineer must obtain a percent composite action from a connector manufacturer, making some engineers uncomfortable. Engineers are dependent upon the recommendations given by the connector manufacturers to establish their designs. This project tested six full-scale sandwich panel walls to evaluate the percent composite action of various connectors and compare the results to those provided by the composite connector manufacturers. This study concluded that the reported degrees of composite action from each manufacturer are considered conservative in all instances for the connectors tested in this paper. Additionally, the intensity and type of connectors are important factors in determining the degree of partial composite action in a panel

Developing a General Methodology for Evaluating Composite Action in Insulated Wall Panels

Precast concrete sandwich wall panels(PCSWPs) have been in use for over 60 years. They provide a very efficient building envelope for many buildings. Characteristic PCSWPs comprise an outer and inner layer (or wythe) of concrete separated by an insulating material. To use all of the material as efficiently as possible, the layers are attached by connectors which penetrate through the insulating layer and are embedded in either concrete wythe. These connectors make it possible for both layers of the wall to work together when resisting loads. The connectors are made out of plastic, or FRP, to prevent heat transfer from one side of the wall to the other. This research evaluated several different FRP systems by fabricating and testing 41small scale “push-off” specimens (3 ft. by 4 ft., 0.91 m by 1.22 m)and eight full-scale sandwich panel walls to evaluate the percent composite action of various connectors and compare the results to those provided by the composite connector manufacturers. Testing of push-off specimens was performed by applying loads perpendicular to the connectors and measuring the amount of deformation that occurred. By determining the load-deformation relationship, engineers can make more informed decisions about the full-scale behavior. This project aimed to validate current procedures using these methods, and to develop simpler, more efficient methods for predicting overall strength of this innovative building system. This study concluded that the reported degrees of composite action from each manufacturer are considered conservative in all instances for the connectors tested. Additionally, the intensity and type of connectors are important factors in determining the degree of partial composite action in a panel. Two methods to predict elastic deformations and cracking were developed(the Beam-Spring model and the Elastic Hand Method) and were compared to the elastic portions of the full-scale testing performed in this study, yielding promising results. Anew method(thePartially-Composite Strength Prediction Method) was also created to predict the nominal moment capacity of concrete sandwich wall panels that is easier to implement than current methodologies and shown to be accurate. The results of this method were also compared to the full-scale testing results in this study.Design and analysis examples using these methods are presented in this report.(243pages

The 2020 National Snow Load Study

The United States has a rich history of snow load studies at the state and national level. The current ASCE 7 snow loads are based on studies performed at the Cold Regions Research and Engineering Laboratory (CRREL) ca. 1980 and updated ca. 1993. The map includes large regions where a site-specific case study is required to establish the load. Many state reports attempt to address the case-study regions designated in the current ASCE 7 design snow load requirements. The independently developed state-specific requirements vary in approach, which can lead to discrepancies in requirements at state boundaries. In addition, there has been great interest to develop site-specific reliability-targeted loads that replace the current load and importance factors applied to 50-year snow load events as defined in ASCE 7-16. This interest stems from the fact that the relative variability in extreme snow load events is not constant across the country, leading to a non-constant probability of failure for a given design scenario. This report describes the creation of a modern, universal, and reproducible approach for estimating reliability-targeted design ground snow loads for the conterminous United States. This new approach significantly reduces the size of case-study regions as currently designated in ASCE 7-16 and resolves discrepancies in design snow load requirements that currently exist along western state boundaries

Structural testing of concrete walls on-edge with combined axial and out-of-plane loading

Full-scale testing of structural components can be time consuming and difficult. The design of full- scale slender concrete walls is highly influenced and controlled by second-order and out-of-plane bending loads. Previous experiments on out-plane bending of slender walls and insulated walls have been performed with bending in the direction of gravity (with or against). Additionally, most of the research considering out-of-plane bending does not include an axial load and suffers from inaccurate results due to not simulating the actual loading and constraining conditions or safety issues. This testing method was developed expressly for the determination of slender wall behavior in insulated concrete panels and verified on solid slender walls, which are well understood. The testing setup presented has the following advantages Reduces the risk of cracking panel prior to testing and provides safe and rapid testing. Offers ease of implementation in labs with height restrictions, given sufficient floor space. Integrates axial and lateral uniform loading

Out-of-Plane Flexural Behavior of InsulatedWall Panels Constructed with Large Insulation Thicknesses

Insulated concrete sandwich wall panels (ICSWPs) are gaining popularity as energy regulations become stricter worldwide. ICSWPs are now being constructed with thinner wythes and thicker insulation to keep up with the changing market, which is reducing material costs and increasing thermal and structural efficiency. However, there is a need for adequate experimental testing to validate the current design methods for these new panels. This research aims to provide that validation by comparing the predictions of four different methods with experimental data obtained from six large-scale panels. The study found that while current design methods adequately predict the behavior of thin wythe and thick insulation ICSWPs within the elastic region, they do not accurately predict their ultimate capacity