Criteria for Restoration of Longitudinal Barriers, Phase II (2021) / Chapter Skim
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155 CHAPTER 8 – EVALUATION OF GUARDRAIL POST DETERIORATION FOR THE G4(2W) The guardrail post is a fundamental component of a guardrail system and its response during a crash event is important to the overall performance of the system.
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156 Scope The scope of this study included: (1) obtaining field-extracted wood guardrail posts from State DOT maintenance garages, (2)
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157 Resistograph Measurements and Processing Resistograph Measurements The deterioration of each post was measured using an IML Resi-F400 S Resistograph, shown in Figure 105. The resistograph was equipped with a 1/16 inch in diameter drilling needle 19 5/16 inches long.
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158 Figure 106. Schematic of typical (a)
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159 Figure 107. Schematic illustrating internal force distribution through cross-section of a circular shaped post.
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160 this location are assumed to be the same as that measured at Point 1 (outer most data point circled in Figure 109) , which was taken directly from the resistograph data.
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161 𝑈 = ∫ 𝜎𝜀𝑑𝑉 ≈ ∑ 𝐴𝑖𝜎𝑖𝜖𝑖 = 𝑖 ∑ ∑ 𝐴𝑖𝑗 𝑖 𝑗 𝐸𝑗𝜖𝑖 2 = ∑ ∑ 𝐴𝑖𝑗 𝑖 𝑗 𝐸𝑗 𝑦𝑖 2 𝑅2 𝜖𝑅 2 𝑖𝑖 Where 𝜎𝑖, 𝜖𝑖and Ei are the stress, strain and modulus, respectively, of the wood post at each increment through the cross-section. Thus, a pseudo strain energy can be computed for the post by substituting E*
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162 Figure 111. Cumulative distribution plot for U*
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163 Pendulum Testing of Post-in-Rigid-Foundation Scope Pendulum tests were conducted at the FOIL to assess the dynamic failure properties of the deteriorated posts. Two series of tests were performed.
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164 Table 39. Test Series 13009 Group 1 (2,372-lb pendulum, velocity = 20 mph, impact point = 21.5 inches)
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165 Table 40. Test Series 13009 Group 2 (2,372-lb pendulum, velocity = 10 mph, impact point = 21.5 inches)
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166 Table 40.
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167 Figure 113. Photo of post specimen soaking in tank of water.
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168 Equipment and Instrumentation Pendulum Device The striker for the tests was a 2,372-lb concrete pendulum with a semi-rigid nose, as shown in Figure 115. The semi-rigid nose, which was developed by researchers from Virginia Tech during the first phase of this study, was fabricated from a wooden block and covered with sheet metal.
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169 Figure 116. Schematic of the accelerometer instrumentation for the pendulum tests.
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170 Figure 117. High-speed camera specifications and placement.
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171 Results The x-channel accelerometer data was processed to obtain the accelerations of the pendulum during impact with the posts. The data was filtered using an SAE Class 60 filter with a cutoff frequency of 100 Hz.
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172 Test Series 13009 Group 1 (20 mph Impact Speed) Table 41 provides the peak force, the strain energy at initiation of rupture, peak moment, and the energy at complete rupture for each post in Test Series 1.
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173 Table 41. Test Results for Test Series 13009 Group 1 (2,372-lb pendulum, velocity = 20 mph, impact point = 21.5 inches)
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174 Test Series 13009 Group 2 (10 mph Impact Speed) Table 42 provides the peak force, the strain energy at initiation of rupture, peak moment, and the energy at complete rupture for each post in Test Series 13009 Group 2.
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175 Table 42. Test Results for Test Series 13009 Group 2 (2,372-lb pendulum, velocity = 10 mph, impact point = 21.5 inches)
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176 Table 42.
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177 Table 43. Statistics for Post Strength Capacity from Pendulum Test Series 13009 (Group 2)
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178 Figure 122. Cumulative distribution plot for the total energy absorbed by the post at complete rupture measured in Test Series 13009 (Group 2)
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179 Figure 124. Peak Moment vs.
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180 Figure 126. Rupture Energy vs.
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181 Figure 127. Test Summary Sheet for Test 13009Q1.
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182 Figure 128. Test Summary Sheet for Test 13009S1.
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183 Figure 129. Peak Force vs.
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184 Figure 131. Test Summary Sheet for Test 13009T1.
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185 Figure 132. Test summary sheet for Test 13009Y1.
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186 Quantifying Wood Post Deterioration Damage Levels The pendulum impact tests conducted in Test Series 13009 were used to establish four levels of damage for deteriorated guardrail posts. For the assessment, only those tests with post diameters ranging from 8.0 to 8.2 inches were selected in order to eliminate the effects of post size.
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187 Table 44. Deterioration damage levels for posts in Test 13009 Series 2 based on strain energy.
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188 Figure 133. Pendulum impact tests from Series 13009 corresponding to deterioration damage level 1 (DL1)
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189 Table 45. Damage levels for guardrail post deterioration.
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190 Figure 137. Graphical representation of damage levels with respect to resi-score, SM, and load capacity.
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191 Visual and Auditory Cues If strength and/or deterioration measurement tools are not available, then visual inspection and "sounding" procedures should be utilized by experienced maintenance personnel to assess the soundness of the posts. Refer to Figure 136 in regard to the following damage assessment cues.
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192 The soil for all tests conformed to Grading B of AASHTO M147-95 and was compacted in 6-inch lifts using a pneumatic tamper. The density, moisture content and degree of compaction of the soil was measured in front of and behind the post after each compaction process using a Troxler-model 3440 Surface Moisture-Density Gauge.
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193 Table 46. Post-in-Soil Test Group 1 (2,372-lb pendulum, v = 20 mph, impact point = 24.88 inches, embedment 40 inches)
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194 Soil Strength Tests Preliminary Tests The first three tests (i.e., 13010A, 13010B and 13010C) involved wooden posts selected from the lot of used posts obtained from the Ohio DOT.
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195 impact force of 12.3 kips with total energy absorption of 86.6 kip-in. The results clearly show that for 96 percent soil compaction (i.e., soil conditions used in the preliminary tests)
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196 Round Wood Post Tests Tests 13010G, 13010H and 13010I were performed using a round wood posts. Test 13010G involved a 68-inch long post with a low level of deterioration (e.g., Resi Scores SM = 0.86 and SU = 0.97)
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197 Figure 142. Summary sheet for Test 13010G.
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198 Figure 143. Summary sheet for Test 13010H.
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199 Figure 144. Summary sheet for Test 13010I.
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200 Figure 145 shows a plot of section modulus vs. post diameter for the round wood post.
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201 Figure 145. Section modulus for round posts with radius ranging from 7 to 8 inches compared to the 6x8 rectangular post.
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202 Table 48. Material properties for wood post model corresponding to damage levels 1 through 3.
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203 Figure 146. Finite element model used for calibrating material property values for various deterioration levels of wood posts.
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204 Figure 148. Energy vs.
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205 Figure 150. Energy vs.
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206 Figure 151. Sequential views of Test 13009H1 and FE analysis DL1(a)
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207 Figure 152. Sequential views for Test 13009L1 and FE analysis DL1(b)
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208 Damage Level 2 (DL2) A single set of material properties were developed for simulating damage level 2.
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209 Figure 154. Energy vs.
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210 Figure 155. Force vs.
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211 Figure 157. Energy vs.
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212 Evaluate Effects of Post Deterioration on Guardrail Performance The effects of post strength degradation on the crash performance of the G4(2W) guardrail was evaluated using FEA.
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213 Figure 159. Analysis setup for evaluation of uniform deterioration of posts in the impact region.
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214 connection; particularly for cases DL2 and DL3. Thus, the results for the deteriorated post cases would likely have been more severe had critical impact conditions been used.
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215 Figure 161. Summary of anchor displacement at rail height from analysis of uniform post deterioration.
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216 Figure 162. Effective plastic strain contour plot for w-beam in splice connection at Post 16.
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217 Table 51. Summary of occupant risk measures from evaluation of uniform post deterioration analyses.
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218 Figure 163. Summary of occupant impact velocity evaluation of uniform post deterioration.
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219 Figure 165. Summary of 50-ms running average acceleration evaluation of uniform post deterioration.
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220 Deteriorated Posts Upstream of Undamaged Posts The analysis model used for evaluating the effects of deteriorated posts upstream of undamaged posts is shown in Figure 167. Figure 167.
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221 Table 52. Summary of barrier damage evaluation from mixed post deterioration analyses.
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222 Figure 169. Summary of anchor displacement at rail height from mixed post deterioration analyses.
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223 Table 53. Summary of occupant risk measures from mixed post deterioration analyses.
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224 Figure 170. Summary of occupant impact velocity evaluation of uniform post deterioration.
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225 Figure 172. Summary of 50-ms running average acceleration evaluation of uniform post deterioration.
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226 Summary and Discussion The purpose of this study task was to quantify the effects of various levels of wood post deterioration on the crash performance of the G4(2W) strong-post guardrail system.
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227 to equipment cost and complexity of this method it may not be feasible for use in routine maintenance assessments for quantifying the degree of post degradation; thus future work should include development of more practical procedures for quantifying post deterioration. Pendulum impact tests were also performed to evaluate the effects of various levels of post deterioration on the impact response of the post-soil system.
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228 deterioration levels increased, while the loading on the upstream anchor was somewhat more notable. The potential for pocketing was higher for this damage scenario and increased as post deterioration levels increased.
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229 Table 54. Recommendations for wood post deterioration damage.
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