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143 | %% --- Materials ---
ops.wipe();
ops.model('basic', '-ndm', 3, '-ndf', 6);
ops.uniaxialMaterial('Concrete02', 2, -35, -0.005, -8.75, 0.02, 0.1, 2.0, 2000);
ops.uniaxialMaterial('Concrete02', 3, -30, -0.003, -6.0, 0.01, 0.1, 2.0, 2000);
ops.uniaxialMaterial('Steel02', 4, 400, 2.0e5, 0.01, 18, 0.925, 0.15);
%% --- Geometry: rectangular double-cell hollow box ---
% This example creates a double-cell hollow box section using MATLAB
% built-in polyshape operations. The section is divided into:
% 1) confined core concrete,
% 2) unconfined cover concrete,
% 3) longitudinal rebars placed along offset boundary paths.
% Overall section dimensions.
B = 2400; % Total section width in the y-direction
H = 1600; % Total section height in the z-direction
% Void dimensions and locations.
voidB = 800; % Width of each rectangular void
voidH = 1100; % Height of each rectangular void
voidCy = 600; % Distance from section center to each void center
% Rebar layout parameters.
barGap = 180; % Target spacing of rebars along each boundary path
rebarR = 12.5; % Rebar radius, e.g., D25 bar
% Cover and mesh parameters.
coverThick = 40; % Clear concrete cover thickness
barCover = coverThick + rebarR; % Distance from concrete face to rebar center
meshSize = 80; % Target mesh size for triangular meshing
% Create the outer rectangular boundary.
outerPoly = polyshape( ...
[-B/2, B/2, B/2, -B/2], ...
[-H/2, -H/2, H/2, H/2]);
% Create the left rectangular void.
void1 = polyshape( ...
[-voidCy-voidB/2, -voidCy+voidB/2, -voidCy+voidB/2, -voidCy-voidB/2], ...
[-voidH/2, -voidH/2, voidH/2, voidH/2]);
% Create the right rectangular void.
void2 = polyshape( ...
[ voidCy-voidB/2, voidCy+voidB/2, voidCy+voidB/2, voidCy-voidB/2], ...
[-voidH/2, -voidH/2, voidH/2, voidH/2]);
% Combine the two voids into one polyshape object.
voids = union([void1; void2]);
% Concrete wall region = outer box minus the two voids.
wallRegion = subtract(outerPoly, voids);
% Offset the outer boundary inward by coverThick.
% This defines the inner limit of the outer cover layer.
outerCoreLimit = polybuffer(outerPoly, -coverThick, 'JointType', 'miter');
% Offset each void boundary outward by coverThick.
% These regions represent the cover concrete around the inner void faces.
voidCover1 = polybuffer(void1, coverThick, 'JointType', 'miter');
voidCover2 = polybuffer(void2, coverThick, 'JointType', 'miter');
voidCovers = union([voidCover1; voidCover2]);
% Confined core = wall concrete inside the outer core limit,
% excluding the cover zones around the void boundaries.
coreRegion = intersect(wallRegion, outerCoreLimit);
coreRegion = subtract(coreRegion, voidCovers);
% Unconfined cover = remaining concrete outside the confined core.
coverRegion = subtract(wallRegion, coreRegion);
%% --- Parts ---
% Each part is assigned an OpenSees material tag and an independent mesh size.
clear parts
parts(1).name = 'Confined core';
parts(1).matTag = 2;
parts(1).geometry = coreRegion;
parts(1).meshSize = meshSize+10; % slightly coarser mesh for core concrete
parts(2).name = 'Unconfined cover';
parts(2).matTag = 3;
parts(2).geometry = coverRegion;
parts(2).meshSize = meshSize; % finer mesh for cover regions
%% --- Rebars using offset boundary + lineRebars ---
% Rebar centerlines are generated by offsetting concrete boundaries.
% The offset distance is coverThick + rebar radius, so that the clear cover
% from concrete face to rebar surface is approximately coverThick.
% Outer rebar path: offset the outer boundary inward.
outerBarPath = polybuffer(outerPoly, -barCover, 'JointType', 'miter');
% Inner rebar paths: offset void boundaries outward into the concrete walls.
innerBarPath1 = polybuffer(void1, barCover, 'JointType', 'miter');
innerBarPath2 = polybuffer(void2, barCover, 'JointType', 'miter');
% Extract boundary vertices from the offset paths.
[yOuter, zOuter] = boundary(outerBarPath);
[yIn1, zIn1] = boundary(innerBarPath1);
[yIn2, zIn2] = boundary(innerBarPath2);
% Generate rebar coordinates along each closed path.
% lineRebars guarantees that all path vertices are occupied by rebars and
% inserts additional bars along each segment according to the target gap.
outerBars = fs.lineRebars(yOuter, zOuter, gap=barGap, closed=true);
innerBars1 = fs.lineRebars(yIn1, zIn1, gap=barGap, closed=true);
innerBars2 = fs.lineRebars(yIn2, zIn2, gap=barGap, closed=true);
% Merge all bar coordinates and remove duplicates at overlapping vertices.
allBarCoords = unique([outerBars; innerBars1; innerBars2], 'rows');
clear rebars
rebars(1).name = 'HRB400 D25';
rebars(1).matTag = 4;
rebars(1).coords = allBarCoords;
rebars(1).area = pi * rebarR^2;
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